+
Intel |
+
X86 |
+
Linux 1.2.8, ELF |
+
+
+
1.5. Outline of This Manual
+ From now on, We will use POSTGRES to mean POSTGRES95.
+ The first part of this manual goes over some basic sys-
+ tem concepts and procedures for starting the POSTGRES
+ system. We then turn to a tutorial overview of the
+ POSTGRES data model and SQL query language, introducing
+ a few of its advanced features. Next, we explain the
+ POSTGRES approach to extensibility and describe how
+ users can extend POSTGRES by adding user-defined types,
+ operators, aggregates, and both query language and pro-
+ gramming language functions. After an extremely brief
+ overview of the POSTGRES rule system, the manual
+ concludes with a detailed appendix that discusses some of
+ the more involved and operating system-specific
+ procedures involved in extending the system.
+
+UNIX is a trademark of X/Open, Ltd. Sun4, SPARC, SunOS
+and Solaris are trademarks of Sun Microsystems, Inc. DEC,
+DECstation, Alpha AXP and ULTRIX are trademarks of Digital
+Equipment Corp. PA-RISC and HP-UX are trademarks of
+Hewlett-Packard Co. OSF/1 is a trademark of the Open
+
+ We assume proficiency with UNIX and C programming.
+
+
+
+[ Previous ]
+
+
+
--- /dev/null
+
+
+
The POSTGRES95 User Manual - LIBPQ
+
+
+
+
+
+
+
+
12. LIBPQ
+
+ LIBPQ is the application programming interface to POSTGRES.
+ LIBPQ is a set of library routines which allows
+ client programs to pass queries to the POSTGRES backend
+ server and to receive the results of these queries.
+ This version of the documentation describes the C
+ interface library. Three short programs are included
+ at the end of this section to show how to write programs that use LIBPQ.
+ There are several examples of LIBPQ applications in the
+ following directories:
+
+ ../src/test/examples
+ ../src/bin/psql
+
+ Frontend programs which use LIBPQ must include the
+ header file libpq-fe.h and must link with the libpq
+ library.
+
+
12.1. Control and Initialization
+ The following environment variables can be used to set
+ up default environment values to avoid hard-coding
+ database names into an application program:
+
+
PGHOST sets the default server name.
+
PGOPTIONS sets additional runtime options for the POSTGRES backend.
+
PGPORT sets the default port for communicating with the POSTGRES backend.
+
PGTTY sets the file or tty on which debugging messages from the backend server are displayed.
+
PGDATABASE sets the default POSTGRES database name.
+
PGREALM sets the Kerberos realm to use with POSTGRES, if it is different from the local realm. If
+
PGREALM is set, POSTGRES applications will attempt
+ authentication with servers for this realm and use
+ separate ticket files to avoid conflicts with local
+ ticket files. This environment variable is only
+ used if Kerberos authentication is enabled.
+
+
+
12.2. Database Connection Functions
+ The following routines deal with making a connection to
+ a backend from a C program.
+
+
PQsetdb
+
Makes a new connection to a backend.
+
PGconn *PQsetdb(char *pghost,
+ char *pgport,
+ char *pgoptions,
+ char *pgtty,
+ char *dbName);
+
+
If any argument is NULL, then the corresponding
+ environment variable is checked. If the environment variable is also not set, then hardwired
+ defaults are used.
+
PQsetdb always returns a valid PGconn pointer.
+
The PQstatus (see below) command should be called
+ to ensure that a connection was properly made
+ before queries are sent via the connection. LIBPQ
+ programmers should be careful to maintain the
+
PGconn abstraction. Use the accessor functions
+ below to get at the contents of PGconn. Avoid
+ directly referencing the fields of the PGconn
+ structure as they are subject to change in the
+ future.
+
PQdb
+
Returns the database name of the connection.
+
char *PQdb(PGconn *conn)
+
+
PQhost
+
Returns the host name of the connection.
+
char *PQhost(PGconn *conn)
+
+
PQoptions
+
Returns the pgoptions used in the connection.
+
char *PQoptions(PGconn *conn)
+
+
PQport
+
Returns the pgport of the connection.
+
char *PQport(PGconn *conn)
+
+
PQtty
+
Returns the pgtty of the connection.
+
char *PQtty(PGconn *conn)
+
+
PQstatus
+
Returns the status of the connection.
+
The status can be CONNECTION_OK or CONNECTION_BAD.
+
ConnStatusType *PQstatus(PGconn *conn)
+
+
PQerrorMessage
+
Returns the error message associated with the connection
+
char *PQerrorMessage(PGconn* conn);
+
+
+
PQfinish
+
Close the connection to the backend. Also frees
+ memory used by the PGconn structure. The PGconn
+ pointer should not be used after PQfinish has been
+ called.
+
void PQfinish(PGconn *conn)
+
+
PQreset
+
Reset the communication port with the backend.
+ This function will close the IPC socket connection
+ to the backend and attempt to reestablish a new
+ connection to the same backend.
+
void PQreset(PGconn *conn)
+
+
PQtrace
+
Enables tracing of messages passed between the
+ frontend and the backend. The messages are echoed
+ to the debug_port file stream.
+
void PQtrace(PGconn *conn,
+ FILE* debug_port);
+
+
PQuntrace
+
Disables tracing of messages passed between the
+ frontend and the backend.
+
void PQuntrace(PGconn *conn);
+
+
+
12.3. Query Execution Functions
+
PQexec
+
Submit a query to POSTGRES. Returns a PGresult
+ pointer if the query was successful or a NULL otherwise. If a NULL is returned, PQerrorMessage can
+ be used to get more information about the error.
+
PGresult *PQexec(PGconn *conn,
+ char *query);
+
+
The PGresult structure encapsulates the query
+ result returned by the backend. LIBPQ programmers
+ should be careful to maintain the PGresult
+ abstraction. Use the accessor functions described
+ below to retrieve the results of the query. Avoid
+ directly referencing the fields of the PGresult
+ structure as they are subject to change in the
+ future.
+
PQresultStatus
+
Returns the result status of the query. PQresultStatus can return one of the following values:
+ PGRES_COMMAND_OK, /* the query was a command */
+ PGRES_TUPLES_OK, /* the query successfully returned tuples */
+ PGRES_COPY_OUT,
+ PGRES_COPY_IN,
+ PGRES_BAD_RESPONSE, /* an unexpected response was received */
+ PGRES_NONFATAL_ERROR,
+ PGRES_FATAL_ERROR
+
+
If the result status is PGRES_TUPLES_OK, then the
+ following routines can be used to retrieve the
+ tuples returned by the query.
+
PQntuples returns the number of tuples (instances)
+ in the query result.
+
+
int PQntuples(PGresult *res);
+
+
PQnfields
+
Returns the number of fields
+ (attributes) in the query result.
+
+
int PQnfields(PGresult *res);
+
+
PQfname
+
Returns the field (attribute) name associated with the given field index. Field indices
+ start at 0.
+
+
char *PQfname(PGresult *res,
+ int field_index);
+
+
PQfnumber
+
Returns the field (attribute) index
+ associated with the given field name.
+
+
int PQfnumber(PGresult *res,
+ char* field_name);
+
+
PQftype
+
Returns the field type associated with the
+ given field index. The integer returned is an
+ internal coding of the type. Field indices start
+ at 0.
+
+
Oid PQftype(PGresult *res,
+ int field_num);
+
+
PQfsize
+
Returns the size in bytes of the field
+ associated with the given field index. If the size
+ returned is -1, the field is a variable length
+ field. Field indices start at 0.
+
+
int2 PQfsize(PGresult *res,
+ int field_index);
+
+
PQgetvalue
+
Returns the field (attribute) value.
+ For most queries, the value returned by PQgetvalue
+ is a null-terminated ASCII string representation
+ of the attribute value. If the query was a result
+ of a BINARY cursor, then the value returned by
+ PQgetvalue is the binary representation of the
+ type in the internal format of the backend server.
+ It is the programmer's responsibility to cast and
+ convert the data to the correct C type. The value
+ returned by PQgetvalue points to storage that is
+ part of the PGresult structure. One must explicitly
+ copy the value into other storage if it is to
+ be used past the lifetime of the PGresult structure itself.
+
+
char* PQgetvalue(PGresult *res,
+ int tup_num,
+ int field_num);
+
+
PQgetlength
+
Returns the length of a field
+ (attribute) in bytes. If the field is a struct
+ varlena, the length returned here does not include
+ the size field of the varlena, i.e., it is 4 bytes
+ less.
+
int PQgetlength(PGresult *res,
+ int tup_num,
+ int field_num);
+
+
PQcmdStatus
+ Returns the command status associated with the
+ last query command.
+ char *PQcmdStatus(PGresult *res);
+
+
PQoidStatus
+ Returns a string with the object id of the tuple
+ inserted if the last query is an INSERT command.
+ Otherwise, returns an empty string.
+
char* PQoidStatus(PGresult *res);
+
+
PQprintTuples
+ Prints out all the tuples and, optionally, the
+ attribute names to the specified output stream.
+ The programs psql and monitor both use PQprintTuples for output.
+
+ PGresult* res,
+ FILE* fout, /* output stream */
+ int printAttName,/* print attribute names or not*/
+ int terseOutput, /* delimiter bars or not?*/
+ int width /* width of column, variable width if 0*/
+ );
+
+
+
PQclear
+ Frees the storage associated with the PGresult.
+ Every query result should be properly freed when
+ it is no longer used. Failure to do this will
+ result in memory leaks in the frontend application.
+
void PQclear(PQresult *res);
+
+
+ POSTGRES provides a fast path interface to send function calls to the backend. This is a trapdoor into
+ system internals and can be a potential security hole.
+ Most users will not need this feature.
+
+
PGresult* PQfn(PGconn* conn,
+ int fnid,
+ int *result_buf,
+ int *result_len,
+ int result_is_int,
+ PQArgBlock *args,
+ int nargs);
+
+
+ The fnid argument is the object identifier of the function to be executed. result_buf is the buffer in which
+ to load the return value. The caller must have allocated sufficient space to store the return value. The
+ result length will be returned in the storage pointed
+ to by result_len. If the result is to be an integer
+ value, than result_is_int should be set to 1; otherwise
+ it should be set to 0. args and nargs specify the
+ arguments to the function.
+ int len;
+ int isint;
+ union {
+ int *ptr;
+ int integer;
+ } u;
+ } PQArgBlock;
+
+ PQfn always returns a valid PGresult*. The resultStatus should be checked before the result is used. The
+ caller is responsible for freeing the PGresult with
+ PQclear when it is not longer needed.
+
12.5. Asynchronous Notification
+ POSTGRES supports asynchronous notification via the
+ LISTEN and NOTIFY commands. A backend registers its
+ interest in a particular relation with the LISTEN command. All backends listening on a particular relation
+ will be notified asynchronously when a NOTIFY of that
+ relation name is executed by another backend. No
+ additional information is passed from the notifier to
+ the listener. Thus, typically, any actual data that
+ needs to be communicated is transferred through the
+ relation.
+ LIBPQ applications are notified whenever a connected
+ backend has received an asynchronous notification.
+ However, the communication from the backend to the
+ frontend is not asynchronous. Notification comes
+ piggy-backed on other query results. Thus, an application must submit queries, even empty ones, in order to
+ receive notice of backend notification. In effect, the
+ LIBPQ application must poll the backend to see if there
+ is any pending notification information. After the
+ execution of a query, a frontend may call PQNotifies to
+ see if any notification data is available from the
+ backend.
+
PQNotifies
+
returns the notification from a list of unhandled
+ notifications from the backend. Returns NULL if
+ there are no pending notifications from the backend. PQNotifies behaves like the popping of a
+ stack. Once a notification is returned from PQnotifies, it is considered handled and will be
+ removed from the list of notifications.
+
PGnotify* PQNotifies(PGconn *conn);
+
+
+ The second sample program gives an example of the use
+ of asynchronous notification.
+
12.6. Functions Associated with the COPY Command
+ The copy command in POSTGRES has options to read from
+ or write to the network connection used by LIBPQ.
+ Therefore, functions are necessary to access this network connection directly so applications may take full
+ advantage of this capability.
+
PQgetline
+
Reads a newline-terminated line of characters
+ (transmitted by the backend server) into a buffer
+ string of size length. Like fgets(3), this routine copies up to length-1 characters into string.
+ It is like gets(3), however, in that it converts
+ the terminating newline into a null character.
+ PQgetline returns EOF at EOF, 0 if the entire line
+ has been read, and 1 if the buffer is full but the
+ terminating newline has not yet been read.
+ Notice that the application must check to see if a
+ new line consists of the single character ".",
+ which indicates that the backend server has finished sending the results of the copy command.
+ Therefore, if the application ever expects to
+ receive lines that are more than length-1 characters long, the application must be sure to check
+ the return value of PQgetline very carefully.
+ The code in
+
+
+ contains routines that correctly handle the copy
+ protocol.
+
int PQgetline(PGconn *conn,
+ char *string,
+ int length)
+
+
PQputline
+
Sends a null-terminated string to the backend
+ server.
+ The application must explicitly send the single
+ character "." to indicate to the backend that it
+ has finished sending its data.
+
+
void PQputline(PGconn *conn,
+ char *string);
+
+
PQendcopy
+
Syncs with the backend. This function waits until
+ the backend has finished the copy. It should
+ either be issued when the last string has been
+ sent to the backend using PQputline or when the
+ last string has been received from the backend
+ using PGgetline. It must be issued or the backend
+ may get "out of sync" with the frontend. Upon
+ return from this function, the backend is ready to
+ receive the next query.
+ The return value is 0 on successful completion,
+ nonzero otherwise.
+
int PQendcopy(PGconn *conn);
+
+ As an example:
+
PQexec(conn, "create table foo (a int4, b char16, d float8)");
+ PQexec(conn, "copy foo from stdin");
+ PQputline(conn, "3<TAB>hello world<TAB>4.5\n");
+ PQputline(conn,"4<TAB>goodbye world<TAB>7.11\n");
+ ...
+ PQputline(conn,".\n");
+ PQendcopy(conn);
+
+
+
12.7. LIBPQ Tracing Functions
+
PQtrace
+
Enable tracing of the frontend/backend communication to a debugging file stream.
+
void PQtrace(PGconn *conn
+ FILE *debug_port)
+
+
+
PQuntrace
+
Disable tracing started by PQtrace
+
void PQuntrace(PGconn *conn)
+
+
+
12.8. User Authentication Functions
+ If the user has generated the appropriate authentication credentials (e.g., obtaining Kerberos tickets),
+ the frontend/backend authentication process is handled
+ by PQexec without any further intervention. The following routines may be called by LIBPQ programs to tailor the behavior of the authentication process.
+
fe_getauthname
+
Returns a pointer to static space containing whatever name the user has authenticated. Use of this
+ routine in place of calls to getenv(3) or getpwuid(3) by applications is highly recommended, as
+ it is entirely possible that the authenticated
+ user name is not the same as value of the USER
+ environment variable or the user's entry in
+ /etc/passwd.
+
+
char *fe_getauthname(char* errorMessage)
+
+
fe_setauthsvc
+
Specifies that LIBPQ should use authentication
+ service name rather than its compiled-in default.
+
This value is typically taken from a command-line
+ switch.
+
void fe_setauthsvc(char *name,
+ char* errorMessage)
+
+
Any error messages from the authentication
+ attempts are returned in the errorMessage argument.
+
+
+ The query buffer is 8192 bytes long, and queries over
+ that length will be silently truncated.
+
12.10.1. Sample Program 1
+ /*
+ * testlibpq.c
+ * Test the C version of LIBPQ, the POSTGRES frontend library.
+ *
+ *
+ */
+ #include <stdio.h>
+ #include "libpq-fe.h"
+ void
+ exit_nicely(PGconn* conn)
+ {
+ PQfinish(conn);
+ exit(1);
+ }
+ main()
+ {
+ char *pghost, *pgport, *pgoptions, *pgtty;
+ char* dbName;
+ int nFields;
+ int i,j;
+ /* FILE *debug; */
+ PGconn* conn;
+ PGresult* res;
+ /* begin, by setting the parameters for a backend connection
+ if the parameters are null, then the system will try to use
+ reasonable defaults by looking up environment variables
+ or, failing that, using hardwired constants */
+ pghost = NULL; /* host name of the backend server */
+ pgport = NULL; /* port of the backend server */
+ pgoptions = NULL; /* special options to start up the backend server */
+ pgtty = NULL; /* debugging tty for the backend server */
+ dbName = "template1";
+ /* make a connection to the database */
+ conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);
+ /* check to see that the backend connection was successfully made */
+ if (PQstatus(conn) == CONNECTION_BAD) {
+ fprintf(stderr,"Connection to database '%s' failed.0, dbName);
+ fprintf(stderr,"%s",PQerrorMessage(conn));
+ exit_nicely(conn);
+ }
+ /* debug = fopen("/tmp/trace.out","w"); */
+ /* PQtrace(conn, debug); */
+ /* start a transaction block */
+
+ res = PQexec(conn,"BEGIN");
+ if (PQresultStatus(res) != PGRES_COMMAND_OK) {
+ fprintf(stderr,"BEGIN command failed0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+ /* should PQclear PGresult whenever it is no longer needed to avoid
+ memory leaks */
+ PQclear(res);
+ /* fetch instances from the pg_database, the system catalog of databases*/
+ res = PQexec(conn,"DECLARE myportal CURSOR FOR select * from pg_database");
+ if (PQresultStatus(res) != PGRES_COMMAND_OK) {
+ fprintf(stderr,"DECLARE CURSOR command failed0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+ PQclear(res);
+ res = PQexec(conn,"FETCH ALL in myportal");
+ if (PQresultStatus(res) != PGRES_TUPLES_OK) {
+ fprintf(stderr,"FETCH ALL command didn't return tuples properly0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+ /* first, print out the attribute names */
+ nFields = PQnfields(res);
+ for (i=0; i < nFields; i++) {
+ printf("%-15s",PQfname(res,i));
+ }
+ printf("0);
+ /* next, print out the instances */
+ for (i=0; i < PQntuples(res); i++) {
+ for (j=0 ; j < nFields; j++) {
+ printf("%-15s", PQgetvalue(res,i,j));
+ }
+ printf("0);
+ }
+ PQclear(res);
+ /* close the portal */
+ res = PQexec(conn, "CLOSE myportal");
+ PQclear(res);
+ /* end the transaction */
+ res = PQexec(conn, "END");
+ PQclear(res);
+ /* close the connection to the database and cleanup */
+ PQfinish(conn);
+
+ /* fclose(debug); */
+ }
+
+
12.10.2. Sample Program 2
+ /*
+ * testlibpq2.c
+ * Test of the asynchronous notification interface
+ *
+ populate a database with the following:
+ CREATE TABLE TBL1 (i int4);
+ CREATE TABLE TBL2 (i int4);
+ CREATE RULE r1 AS ON INSERT TO TBL1 DO [INSERT INTO TBL2 values (new.i); NOTIFY TBL2];
+ * Then start up this program
+ * After the program has begun, do
+ INSERT INTO TBL1 values (10);
+ *
+ *
+ */
+ #include <stdio.h>
+ #include "libpq-fe.h"
+ void exit_nicely(PGconn* conn)
+ {
+ PQfinish(conn);
+ exit(1);
+ }
+ main()
+ {
+ char *pghost, *pgport, *pgoptions, *pgtty;
+ char* dbName;
+ int nFields;
+ int i,j;
+ PGconn* conn;
+ PGresult* res;
+ PGnotify* notify;
+ /* begin, by setting the parameters for a backend connection
+ if the parameters are null, then the system will try to use
+ reasonable defaults by looking up environment variables
+ or, failing that, using hardwired constants */
+ pghost = NULL; /* host name of the backend server */
+ pgport = NULL; /* port of the backend server */
+ pgoptions = NULL; /* special options to start up the backend server */
+ pgtty = NULL; /* debugging tty for the backend server */
+ dbName = getenv("USER"); /* change this to the name of your test database*/
+ /* make a connection to the database */
+ conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);
+
+ /* check to see that the backend connection was successfully made */
+ if (PQstatus(conn) == CONNECTION_BAD) {
+ fprintf(stderr,"Connection to database '%s' failed.0, dbName);
+ fprintf(stderr,"%s",PQerrorMessage(conn));
+ exit_nicely(conn);
+ }
+ res = PQexec(conn, "LISTEN TBL2");
+ if (PQresultStatus(res) != PGRES_COMMAND_OK) {
+ fprintf(stderr,"LISTEN command failed0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+ /* should PQclear PGresult whenever it is no longer needed to avoid
+ memory leaks */
+ PQclear(res);
+ while (1) {
+ /* async notification only come back as a result of a query*/
+ /* we can send empty queries */
+ res = PQexec(conn, " ");
+ /* printf("res->status = %s0, pgresStatus[PQresultStatus(res)]); */
+ /* check for asynchronous returns */
+ notify = PQnotifies(conn);
+ if (notify) {
+ fprintf(stderr,
+ "ASYNC NOTIFY of '%s' from backend pid '%d' received0,
+ notify->relname, notify->be_pid);
+ free(notify);
+ break;
+ }
+ PQclear(res);
+ }
+ /* close the connection to the database and cleanup */
+ PQfinish(conn);
+ }
+
+
12.10.3. Sample Program 3
+ /*
+ * testlibpq3.c
+ * Test the C version of LIBPQ, the POSTGRES frontend library.
+ * tests the binary cursor interface
+ *
+ *
+ *
+ populate a database by doing the following:
+ CREATE TABLE test1 (i int4, d float4, p polygon);
+ INSERT INTO test1 values (1, 3.567, '(3.0, 4.0, 1.0, 2.0)'::polygon);
+ INSERT INTO test1 values (2, 89.05, '(4.0, 3.0, 2.0, 1.0)'::polygon);
+ the expected output is:
+ tuple 0: got
+ i = (4 bytes) 1,
+ d = (4 bytes) 3.567000,
+ p = (4 bytes) 2 points boundbox = (hi=3.000000/4.000000, lo = 1.000000,2.000000)
+ tuple 1: got
+ i = (4 bytes) 2,
+ d = (4 bytes) 89.050003,
+ p = (4 bytes) 2 points boundbox = (hi=4.000000/3.000000, lo = 2.000000,1.000000)
+ *
+ */
+ #include <stdio.h>
+ #include "libpq-fe.h"
+ #include "utils/geo-decls.h" /* for the POLYGON type */
+ void exit_nicely(PGconn* conn)
+ {
+ PQfinish(conn);
+ exit(1);
+ }
+ main()
+ {
+ char *pghost, *pgport, *pgoptions, *pgtty;
+ char* dbName;
+ int nFields;
+ int i,j;
+ int i_fnum, d_fnum, p_fnum;
+ PGconn* conn;
+ PGresult* res;
+ /* begin, by setting the parameters for a backend connection
+ if the parameters are null, then the system will try to use
+ reasonable defaults by looking up environment variables
+ or, failing that, using hardwired constants */
+ pghost = NULL; /* host name of the backend server */
+ pgport = NULL; /* port of the backend server */
+ pgoptions = NULL; /* special options to start up the backend server */
+ pgtty = NULL; /* debugging tty for the backend server */
+ dbName = getenv("USER"); /* change this to the name of your test database*/
+ /* make a connection to the database */
+ conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);
+ /* check to see that the backend connection was successfully made */
+ if (PQstatus(conn) == CONNECTION_BAD) {
+ fprintf(stderr,"Connection to database '%s' failed.0, dbName);
+ fprintf(stderr,"%s",PQerrorMessage(conn));
+ exit_nicely(conn);
+ }
+ /* start a transaction block */
+ res = PQexec(conn,"BEGIN");
+ if (PQresultStatus(res) != PGRES_COMMAND_OK) {
+ fprintf(stderr,"BEGIN command failed0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+ /* should PQclear PGresult whenever it is no longer needed to avoid
+ memory leaks */
+ PQclear(res);
+ /* fetch instances from the pg_database, the system catalog of databases*/
+ res = PQexec(conn,"DECLARE mycursor BINARY CURSOR FOR select * from test1");
+ if (PQresultStatus(res) != PGRES_COMMAND_OK) {
+ fprintf(stderr,"DECLARE CURSOR command failed0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+ PQclear(res);
+ res = PQexec(conn,"FETCH ALL in mycursor");
+ if (PQresultStatus(res) != PGRES_TUPLES_OK) {
+ fprintf(stderr,"FETCH ALL command didn't return tuples properly0);
+ PQclear(res);
+ exit_nicely(conn);
+ }
+ i_fnum = PQfnumber(res,"i");
+ d_fnum = PQfnumber(res,"d");
+ p_fnum = PQfnumber(res,"p");
+ for (i=0;i<3;i++) {
+ printf("type[%d] = %d, size[%d] = %d0,
+ i, PQftype(res,i),
+ i, PQfsize(res,i));
+ }
+ for (i=0; i < PQntuples(res); i++) {
+ int *ival;
+ float *dval;
+ int plen;
+ POLYGON* pval;
+ /* we hard-wire this to the 3 fields we know about */
+ ival = (int*)PQgetvalue(res,i,i_fnum);
+ dval = (float*)PQgetvalue(res,i,d_fnum);
+ plen = PQgetlength(res,i,p_fnum);
+ /* plen doesn't include the length field so need to increment by VARHDSZ*/
+ pval = (POLYGON*) malloc(plen + VARHDRSZ);
+ pval->size = plen;
+ memmove((char*)&pval->npts, PQgetvalue(res,i,p_fnum), plen);
+ printf("tuple %d: got0, i);
+ printf(" i = (%d bytes) %d,0,
+ PQgetlength(res,i,i_fnum), *ival);
+ printf(" d = (%d bytes) %f,0,
+ PQgetlength(res,i,d_fnum), *dval);
+ printf(" p = (%d bytes) %d points boundbox = (hi=%f/%f, lo = %f,%f)0,
+ PQgetlength(res,i,d_fnum),
+ pval->npts,
+ pval->boundbox.xh,
+ pval->boundbox.yh,
+ pval->boundbox.xl,
+ pval->boundbox.yl);
+ }
+ PQclear(res);
+ /* close the portal */
+ res = PQexec(conn, "CLOSE mycursor");
+ PQclear(res);
+ /* end the transaction */
+ res = PQexec(conn, "END");
+ PQclear(res);
+ /* close the connection to the database and cleanup */
+ PQfinish(conn);
+ }
+
+
+
+
+
+
--- /dev/null
+
+
+
The POSTGRES95 User Manual - LARGE OBJECTS
+
+
+
+
+
+
+
+
13. LARGE OBJECTS
+
+ In POSTGRES, data values are stored in tuples and
+ individual tuples cannot span data pages. Since the size of
+ a data page is 8192 bytes, the upper limit on the size
+ of a data value is relatively low. To support the storage
+ of larger atomic values, POSTGRES provides a large
+ object interface. This interface provides file
+ oriented access to user data that has been declared to
+ be a large type.
+ This section describes the implementation and the
+ programmatic and query language interfaces to POSTGRES
+ large object data.
+
+ Originally, POSTGRES 4.2 supports three standard
+ implementations of large objects: as files external
+ to POSTGRES, as UNIX files managed by POSTGRES, and as data
+ stored within the POSTGRES database. It causes
+ considerable confusion among users. As a result, we only
+ support large objects as data stored within the POSTGRES
+ database in POSTGRES95. Even though is is slower to
+ access, it provides stricter data integrity and time
+ travel. For historical reasons, they are called
+ Inversion large objects. (We will use Inversion and large
+ objects interchangeably to mean the same thing in this
+ section.)
+
+
13.2. Inversion Large Objects
+ The Inversion large object implementation breaks large
+ objects up into "chunks" and stores the chunks in
+ tuples in the database. A B-tree index guarantees fast
+ searches for the correct chunk number when doing random
+ access reads and writes.
+
+
13.3. Large Object Interfaces
+ The facilities POSTGRES provides to access large
+ objects, both in the backend as part of user-defined
+ functions or the front end as part of an application
+ using the interface, are described below. (For users
+ familiar with POSTGRES 4.2, POSTGRES95 has a new set of
+ functions providing a more coherent interface. The
+ interface is the same for dynamically-loaded C
+ functions as well as for .
+ The POSTGRES large object interface is modeled after
+ the UNIX file system interface, with analogues of
+ open(2), read(2), write(2), lseek(2), etc. User
+ functions call these routines to retrieve only the data of
+ interest from a large object. For example, if a large
+ object type called mugshot existed that stored
+ photographs of faces, then a function called beard could
+ be declared on mugshot data. Beard could look at the
+ lower third of a photograph, and determine the color of
+ the beard that appeared there, if any. The entire
+ large object value need not be buffered, or even
+ examined, by the beard function.
+ Large objects may be accessed from dynamically-loaded C
+ functions or database client programs that link the
+ library. POSTGRES provides a set of routines that
+ support opening, reading, writing, closing, and seeking on
+ large objects.
+
13.3.1. Creating a Large Object
+ The routine
+
Oid lo_creat(PGconn *conn, int mode)
+
+ creates a new large object. The mode is a bitmask
+ describing several different attributes of the new
+ object. The symbolic constants listed here are defined
+ in
+
/usr/local/postgres95/src/backend/libpq/libpq-fs.h
+
+ The access type (read, write, or both) is controlled by
+ OR ing together the bits INV_READ and INV_WRITE. If
+ the large object should be archived -- that is, if
+ historical versions of it should be moved periodically to
+ a special archive relation -- then the INV_ARCHIVE bit
+ should be set. The low-order sixteen bits of mask are
+ the storage manager number on which the large object
+ should reside. For sites other than Berkeley, these
+ bits should always be zero.
+ The commands below create an (Inversion) large object:
+
inv_oid = lo_creat(INV_READ|INV_WRITE|INV_ARCHIVE);
+
+
+
13.3.2. Importing a Large Object
+To import a UNIX file as
+ a large object, call
+ lo_import(PGconn *conn, text *filename)
+
+ The filename argument specifies the UNIX pathname of
+ the file to be imported as a large object.
+
13.3.3. Exporting a Large Object
+To export a large object
+ into UNIX file, call
+ lo_export(PGconn *conn, Oid lobjId, text *filename)
+
+ The lobjId argument specifies the Oid of the large
+ object to export and the filename argument specifies
+ the UNIX pathname of the file.
+
13.3.4. Opening an Existing Large Object
+ To open an existing large object, call
+ lo_open(PGconn *conn, Oid lobjId, int mode, ...)
+
+ The lobjId argument specifies the Oid of the large
+ object to open. The mode bits control whether the
+ object is opened for reading INV_READ), writing or
+ both.
+ A large object cannot be opened before it is created.
+ lo_open returns a large object descriptor for later use
+ in lo_read, lo_write, lo_lseek, lo_tell, and lo_close.
+
13.3.5. Writing Data to a Large Object
+ The routine
+ lo_write(PGconn *conn, int fd, char *buf, int len)
+
+ writes len bytes from buf to large object fd. The fd
+ argument must have been returned by a previous lo_open.
+ The number of bytes actually written is returned. In
+ the event of an error, the return value is negative.
+
13.3.6. Seeking on a Large Object
+ To change the current read or write location on a large
+ object, call
+ lo_lseek(PGconn *conn, int fd, int offset, int whence)
+
+ This routine moves the current location pointer for the
+ large object described by fd to the new location specified
+ by offset. The valid values for .i whence are
+ SEEK_SET SEEK_CUR and SEEK_END.
+
13.3.7. Closing a Large Object Descriptor
+ A large object may be closed by calling
+ lo_close(PGconn *conn, int fd)
+
+ where fd is a large object descriptor returned by
+ lo_open. On success, lo_close returns zero. On error,
+ the return value is negative.
+
+
13.4. Built in registered functions
+ There are two built-in registered functions, lo_import
+ and lo_export which are convenient for use in SQL
+ queries.
+ Here is an example of there use
+ name text,
+ raster oid
+ );
+
+ INSERT INTO image (name, raster)
+ VALUES ('beautiful image', lo_import('/etc/motd'));
+
+ SELECT lo_export(image.raster, "/tmp/motd") from image
+ WHERE name = 'beautiful image';
+
+
13.5. Accessing Large Objects from LIBPQ
+ Below is a sample program which shows how the large object
+ interface
+ in LIBPQ can be used. Parts of the program are
+ commented out but are left in the source for the readers
+ benefit. This program can be found in
+
+ Frontend applications which use the large object interface
+ in LIBPQ should include the header file
+ libpq/libpq-fs.h and link with the libpq library.
+
+
/*--------------------------------------------------------------
+ *
+ * testlo.c--
+ * test using large objects with libpq
+ *
+ * Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ * /usr/local/devel/pglite/cvs/src/doc/manual.me,v 1.16 1995/09/01 23:55:00 jolly Exp
+ *
+ *--------------------------------------------------------------
+ */
+ #include <stdio.h>
+ #include "libpq-fe.h"
+ #include "libpq/libpq-fs.h"
+ #define BUFSIZE 1024
+ /*
+ * importFile * import file "in_filename" into database as large object "lobjOid"
+ *
+ */
+ Oid importFile(PGconn *conn, char *filename)
+ {
+ Oid lobjId;
+ int lobj_fd;
+ char buf[BUFSIZE];
+ int nbytes, tmp;
+ int fd;
+ /*
+ * open the file to be read in
+ */
+ fd = open(filename, O_RDONLY, 0666);
+ if (fd < 0) { /* error */
+ fprintf(stderr, "can't open unix file
+ }
+ /*
+ * create the large object
+ */
+ lobjId = lo_creat(conn, INV_READ|INV_WRITE);
+ if (lobjId == 0) {
+ fprintf(stderr, "can't create large object");
+ }
+ lobj_fd = lo_open(conn, lobjId, INV_WRITE);
+ /*
+ * read in from the Unix file and write to the inversion file
+ */
+ while ((nbytes = read(fd, buf, BUFSIZE)) > 0) {
+ tmp = lo_write(conn, lobj_fd, buf, nbytes);
+ if (tmp < nbytes) {
+ fprintf(stderr, "error while reading
+ }
+ }
+ (void) close(fd);
+ (void) lo_close(conn, lobj_fd);
+ return lobjId;
+ }
+ void pickout(PGconn *conn, Oid lobjId, int start, int len)
+ {
+ int lobj_fd;
+ char* buf;
+ int nbytes;
+ int nread;
+ lobj_fd = lo_open(conn, lobjId, INV_READ);
+ if (lobj_fd < 0) {
+ fprintf(stderr,"can't open large object %d",
+ lobjId);
+ }
+ lo_lseek(conn, lobj_fd, start, SEEK_SET);
+ buf = malloc(len+1);
+ nread = 0;
+ while (len - nread > 0) {
+ nbytes = lo_read(conn, lobj_fd, buf, len - nread);
+ buf[nbytes] = ' ';
+ fprintf(stderr,">>> %s", buf);
+ nread += nbytes;
+ }
+ fprintf(stderr,"0);
+ lo_close(conn, lobj_fd);
+ }
+ void overwrite(PGconn *conn, Oid lobjId, int start, int len)
+ {
+ int lobj_fd;
+ char* buf;
+ int nbytes;
+ int nwritten;
+ int i;
+ lobj_fd = lo_open(conn, lobjId, INV_READ);
+ if (lobj_fd < 0) {
+ fprintf(stderr,"can't open large object %d",
+ lobjId);
+ }
+ lo_lseek(conn, lobj_fd, start, SEEK_SET);
+ buf = malloc(len+1);
+ for (i=0;i<len;i++)
+ buf[i] = 'X';
+ buf[i] = ' ';
+ nwritten = 0;
+ while (len - nwritten > 0) {
+ nbytes = lo_write(conn, lobj_fd, buf + nwritten, len - nwritten);
+ nwritten += nbytes;
+ }
+ fprintf(stderr,"0);
+ lo_close(conn, lobj_fd);
+ }
+
+ /*
+ * exportFile * export large object "lobjOid" to file "out_filename"
+ *
+ */
+ void exportFile(PGconn *conn, Oid lobjId, char *filename)
+ {
+ int lobj_fd;
+ char buf[BUFSIZE];
+ int nbytes, tmp;
+ int fd;
+ /*
+ * create an inversion "object"
+ */
+ lobj_fd = lo_open(conn, lobjId, INV_READ);
+ if (lobj_fd < 0) {
+ fprintf(stderr,"can't open large object %d",
+ lobjId);
+ }
+ /*
+ * open the file to be written to
+ */
+ fd = open(filename, O_CREAT|O_WRONLY, 0666);
+ if (fd < 0) { /* error */
+ fprintf(stderr, "can't open unix file
+ filename);
+ }
+ /*
+ * read in from the Unix file and write to the inversion file
+ */
+ while ((nbytes = lo_read(conn, lobj_fd, buf, BUFSIZE)) > 0) {
+ tmp = write(fd, buf, nbytes);
+ if (tmp < nbytes) {
+ fprintf(stderr,"error while writing
+ filename);
+ }
+ }
+ (void) lo_close(conn, lobj_fd);
+ (void) close(fd);
+ return;
+ }
+ void
+ exit_nicely(PGconn* conn)
+ {
+ PQfinish(conn);
+ exit(1);
+ }
+ int
+ main(int argc, char **argv)
+ {
+ char *in_filename, *out_filename;
+ char *database;
+ Oid lobjOid;
+ PGconn *conn;
+ PGresult *res;
+ if (argc != 4) {
+ fprintf(stderr, "Usage: %s database_name in_filename out_filename0,
+ argv[0]);
+ exit(1);
+ }
+ database = argv[1];
+ in_filename = argv[2];
+ out_filename = argv[3];
+ /*
+ * set up the connection
+ */
+ conn = PQsetdb(NULL, NULL, NULL, NULL, database);
+ /* check to see that the backend connection was successfully made */
+ if (PQstatus(conn) == CONNECTION_BAD) {
+ fprintf(stderr,"Connection to database '%s' failed.0, database);
+ fprintf(stderr,"%s",PQerrorMessage(conn));
+ exit_nicely(conn);
+ }
+ res = PQexec(conn, "begin");
+ PQclear(res);
+
+ printf("importing file
+ /* lobjOid = importFile(conn, in_filename); */
+ lobjOid = lo_import(conn, in_filename);
+ /*
+ printf("as large object %d.0, lobjOid);
+ printf("picking out bytes 1000-2000 of the large object0);
+ pickout(conn, lobjOid, 1000, 1000);
+ printf("overwriting bytes 1000-2000 of the large object with X's0);
+ overwrite(conn, lobjOid, 1000, 1000);
+ */
+ printf("exporting large object to file
+ /* exportFile(conn, lobjOid, out_filename); */
+ lo_export(conn, lobjOid,out_filename);
+ res = PQexec(conn, "end");
+ PQclear(res);
+ PQfinish(conn);
+ exit(0);
+ }
+
+
+
+
+
+
--- /dev/null
+
+
+
The POSTGRES95 User Manual
+
+
+
+
+The
+POSTGRES95 User Manual
+
+
+ Version 1.0 (September 5, 1995)
+
+ and
+ (with the POSTGRES Group)
+ Computer Science Div., Dept. of EECS
+ University of California at Berkeley
+
+
+Table of Contents
+
1.1. A Short History of POSTGRES+
1.2. What is POSTGRES95?+
1.4. About This Release+
1.5. Outline of This Manual+
+
2. ARCHITECTURE CONCEPTS+
3.1. Setting Up Your Enviroment+
3.2. Starting The Postmaster+
3.3. Adding And Deleting Users+
3.4. Starting Applications+
3.5. Managing A Database+
3.5.1. Creating A Database+
3.5.2. Accessing A Database+
3.5.3. Destroying A Database+
+
+
4.2. Creating a New Class+
4.3. Populating a Class with Instances+
4.5. Redirecting SELECT Queries+
+
5. ADVANCED POSTGRES SQL FEATURES+
+
+
6. EXTENDING SQL: AN OVERVIEW+
6.1. How Extensibility Works+
6.2. The POSTGRES Type System+
6.3. About the POSTGRES System Catalogs+
+
7. EXTENDING SQL: FUNCTIONS+
7.1. Query Language (SQL) Functions+
7.1.1. SQL Functions on Base Types+
+
7.2. Programming Language Functions+
7.2.1. Programming Language Functions on Base Types+
7.2.2. Programming Language Functions on Composite Types+
+
+
8. EXTENDING SQL: TYPES+
8.1. User-Defined Types+
8.1.1. Functions Needed for a User-Defined Type+
+
+
9. EXTENDING SQL: OPERATORS+
+
10. EXTENDING SQL: AGGREGATES+
+
11. INTERFACING EXTENSIONS TO INDICES+
+
12.1. Control and Initialization+
12.2. Database Connection Functions+
12.3. Query Execution Functions+
12.5. Asynchronous Notification+
12.6. Functions Associated with the COPY Command+
12.7. LIBPQ Tracing Functions+
12.8. User Authentication Functions+
12.10.1. Sample Program 1+
12.10.2. Sample Program 2+
12.10.3. Sample Program 3+
+
+
13.2. Inversion Large Objects+
13.3. Large Object Interfaces+
13.3.1. Creating a Large Object+
13.3.2. Importing a Large Object+
13.3.3. Exporting a Large Object+
13.3.4. Opening an Existing Large Object+
13.3.5. Writing Data to a Large Object+
13.3.6. Seeking on a Large Object+
13.3.7. Closing a Large Object Descriptor+
+
13.4. Built in registered functions+
13.5. Accessing Large Objects from LIBPQ+
+
14. THE POSTGRES RULE SYSTEM+
15. ADMINISTERING POSTGRES+
Appendix A: Linking Dynamically-Loaded Functions+
+
+
+
HyperNews Forum - About this Manual.+
+
POSTGRES95 is copyright © 1994-5 by the Regents of the+University of California.
+Converted to HTML by
J. Douglas Dunlop +The file
+pg95user.tgz contains the complete manual for download.
+
+
--- /dev/null
+
+
+
The POSTGRES95 User Manual - THE QUERY LANGUAGE
+
+
+
+
+
+
+
+
4. THE QUERY LANGUAGE
+
+ The POSTGRES query language is a variant of SQL-3. It
+ has many extensions such as an extensible type system,
+ inheritance, functions and production rules. Those are
+ features carried over from the original POSTGRES query
+ language, POSTQUEL. This section provides an overview
+ of how to use POSTGRES SQL to perform simple operations.
+ This manual is only intended to give you an idea of our
+ flavor of SQL and is in no way a complete tutorial on
+ SQL. Numerous books have been written on SQL. For
+ instance, consult
[MELT93] or +
[DATE93]. You should also+ be aware that some features are not part of the ANSI
+ standard.
+ In the examples that follow, we assume that you have
+ created the mydb database as described in the previous
+ subsection and have started psql.
+ Examples in this manual can also be found in
+ /usr/local/postgres95/src/tutorial. Refer to the
+ README file in that directory for how to use them. To
+ start the tutorial, do the following:
+
% cd /usr/local/postgres95/src/tutorial
+ % psql -s mydb
+ Welcome to the POSTGRES95 interactive sql monitor:
+
+ type \? for help on slash commands
+ type \q to quit
+ type \g or terminate with semicolon to execute query
+ You are currently connected to the database: jolly
+
+
+ mydb=> \i basics.sql
+
+ The \i command read in queries from the specified
+ files. The -s option puts you in single step mode which
+ pauses before sending a query to the backend. Queries
+ in this section are in the file basics.sql.
+
+ The fundamental notion in POSTGRES is that of a class,
+ which is a named collection of object instances. Each
+ instance has the same collection of named attributes,
+ and each attribute is of a specific type. Furthermore,
+ each instance has a permanent object identifier (OID)
+ that is unique throughout the installation. Because
+ SQL syntax refers to tables, we will use the terms
+ table< and class interchangeably. Likewise, a row is an
+ instance and columns are attributes.
+ As previously discussed, classes are grouped into
+ databases, and a collection of databases managed by a
+ single postmaster process constitutes an installation
+ or site.
+
+
4.2. Creating a New Class
+ You can create a new class by specifying the class
+ name, along with all attribute names and their types:
+ city varchar(80),
+ temp_lo int, -- low temperature
+ temp_hi int, -- high temperature
+ prcp real, -- precipitation
+ date date
+ );
+
+ Note that keywords are case-insensitive but identifiers
+ are case-sensitive. POSTGRES SQL supports the usual
+ SQL types int, float, real, smallint, char(N),
+ varchar(N), date, and time. As we will
+ see later, POSTGRES can be customized with an
+ arbitrary number of
+ user-defined data types. Consequently, type names are
+ not keywords.
+ So far, the POSTGRES create command looks exactly like
+ the command used to create a table in a traditional
+ relational system. However, we will presently see that
+ classes have properties that are extensions of the
+ relational model.
+
+
4.3. Populating a Class with Instances
+ The insert statement is used to populate a class with
+ instances:
+ VALUES ('San Francisco', 46, 50, 0.25, '11/27/1994')
+
+ You can also use the copy command to perform load large
+ amounts of data from flat (ASCII) files.
+
+ The weather class can be queried with normal relational
+ selection and projection queries. A SQL select
+ statement is used to do this. The statement is divided into
+ a target list (the part that lists the attributes to be
+ returned) and a qualification (the part that specifies
+ any restrictions). For example, to retrieve all the
+ rows of weather, type:
+
+
+ and the output should be:
+ +--------------+---------+---------+------+------------+
+ |city | temp_lo | temp_hi | prcp | date |
+ +--------------+---------+---------+------+------------+
+ |San Francisco | 46 | 50 | 0.25 | 11-27-1994 |
+ +--------------+---------+---------+------+------------+
+ |San Francisco | 43 | 57 | 0 | 11-29-1994 |
+ +--------------+---------+---------+------+------------+
+ |Hayward | 37 | 54 | | 11-29-1994 |
+ +--------------+---------+---------+------+------------+
+
+ You may specify any aribitrary expressions in the target list. For example, you can do:
+
* SELECT city, (temp_hi+temp_lo)/2 AS temp_avg, date FROM weather;
+
+ Arbitrary Boolean operators ( and, or and not) are
+ allowed in the qualification of any query. For example,
+ FROM weather
+ WHERE city = 'San Francisco'
+ and prcp > 0.0;
+
+ +--------------+---------+---------+------+------------+
+ |city | temp_lo | temp_hi | prcp | date |
+ +--------------+---------+---------+------+------------+
+ |San Francisco | 46 | 50 | 0.25 | 11-27-1994 |
+ +--------------+---------+---------+------+------------+
+
+
+ As a final note, you can specify that the results of a
+ select can be returned in a sorted order or with duplicate instances removed.
+ FROM weather
+ ORDER BY city;
+
+
+
4.5. Redirecting SELECT Queries
+ Any select query can be redirected to a new class
+
SELECT * INTO temp from weather;
+
+ This creates an implicit create command, creating a new
+ class temp with the attribute names and types specified
+ in the target list of the SELECT INTO command. We can
+ then, of course, perform any operations on the resulting
+ class that we can perform on other classes.
+
+
4.6. Joins Between Classes
+ Thus far, our queries have only accessed one class at a
+ time. Queries can access multiple classes at once, or
+ access the same class in such a way that multiple
+ instances of the class are being processed at the same
+ time. A query that accesses multiple instances of the
+ same or different classes at one time is called a join
+ query.
+ As an example, say we wish to find all the records that
+ are in the temperature range of other records. In
+ effect, we need to compare the temp_lo and temp_hi
+ attributes of each EMP instance to the temp_lo and
+ temp_hi attributes of all other EMP instances.
2 We can+ do this with the following query:
+
SELECT W1.city, W1.temp_lo, W1.temp_hi,
+ W2.city, W2.temp_lo, W2.temp_hi
+ FROM weather W1, weather W2
+ WHERE W1.temp_lo < W2.temp_lo
+ and W1.temp_hi > W2.temp_hi;
+
+ +--------------+---------+---------+---------------+---------+---------+
+ |city | temp_lo | temp_hi | city | temp_lo | temp_hi |
+ +--------------+---------+---------+---------------+---------+---------+
+ |San Francisco | 43 | 57 | San Francisco | 46 | 50 |
+ +--------------+---------+---------+---------------+---------+---------+
+ |San Francisco | 37 | 54 | San Francisco | 46 | 50 |
+ +--------------+---------+---------+---------------+---------+---------+
+
+ In this case, both W1 and W2 are surrogates for an
+ instance of the class weather, and both range over all
+ instances of the class. (In the terminology of most
+ database systems, W1 and W2 are known as "range variables.")
+ A query can contain an arbitrary number of
+ class names and surrogates.
3+
+ You can update existing instances using the update command.
+ Suppose you discover the temperature readings are
+ all off by 2 degrees as of Nov 28, you may update the
+ data as follow:
+ SET temp_hi = temp_hi - 2, temp_lo = temp_lo - 2
+ WHERE date > '11/28/1994;
+
+
+ Deletions are performed using the delete command:
+
* DELETE FROM weather WHERE city = 'Hayward';
+
+ All weather recording belongs to Hayward is removed.
+ One should be wary of queries of the form
+
+ Without a qualification, the delete command will simply
+ delete all instances of the given class, leaving it
+ empty. The system will not request confirmation before
+ doing this.
+
+
4.9. Using Aggregate Functions
+ Like most other query languages, POSTGRES supports
+ aggregate functions. However, the current
+ implementation of POSTGRES aggregate functions is very limited.
+ Specifically, while there are aggregates to compute
+ such functions as the count, sum, average, maximum and
+ minimum over a set of instances, aggregates can only
+ appear in the target list of a query and not in the
+ qualification ( where clause) As an example,
+ FROM weather;
+
+ Aggregates may also have GROUP BY clauses:
+ SELECT city, max(temp_lo)
+ FROM weather
+ GROUP BY city;
+
+
+
2. This is only a conceptual model. The actual join may+ be performed in a more efficient manner, but this is invisible to the user.
+
+
3. The semantics of such a join are + that the qualification
+ is a truth expression defined for the Cartesian product of
+ the classes indicated in the query. For those instances in
+ the Cartesian product for which the qualification is true,
+ POSTGRES computes and returns the values specified in the
+ target list. POSTGRES SQL does not assign any meaning to
+ duplicate values in such expressions. This means that POSTGRES
+ sometimes recomputes the same target list several times
+ this frequently happens when Boolean expressions are connected
+ with an or. To remove such duplicates, you must use
+ the select distinct statement.
+
+
+
+
+
+
--- /dev/null
+
+
+
The POSTGRES95 User Manual - REFERENCES
+
+
+
+
+
+
+
+
16. REFERENCES
+
+
[DATE93]Date, C. J. and Darwen, Hugh, A Guide to The+ SQL Standard, 3rd Edition, Reading, MA, June
+ 1993.
+
[MELT93]Melton, J. Understanding the New SQL, 1994.+
[ONG90]Ong, L. and Goh, J., ``A Unified Framework+ for Version Modeling Using Production Rules
+ in a Database System," Electronics Research
+ Laboratory, University of California, ERL
+ Technical Memorandum M90/33, Berkeley, CA,
+ April 1990.
+
[ROWE87]Rowe, L. and Stonebraker, M., ``The POSTGRES+ Data Model,'' Proc. 1987 VLDB Conference,
+ Brighton, England, Sept. 1987.
+
[STON86]Stonebraker, M. and Rowe, L., ``The Design+ of POSTGRES,'' Proc. 1986 ACM-SIGMOD Conference on Management of Data, Washington, DC,
+ May 1986.
+
[STON87a]Stonebraker, M., Hanson, E. and Hong, C.-H.,+ ``The Design of the POSTGRES Rules System,''
+ Proc. 1987 IEEE Conference on Data Engineering, Los Angeles, CA, Feb. 1987.
+
[STON87b]Stonebraker, M., ``The POSTGRES Storage System,'' Proc. 1987 VLDB Conference, Brighton,+ England, Sept. 1987.
+
[STON89]Stonebraker, M., Hearst, M., and Potamianos,+ S., ``A Commentary on the POSTGRES Rules
+ System,'' SIGMOD Record 18(3), Sept. 1989.
+
[STON90a]Stonebraker, M., Rowe, L. A., and Hirohama,+ M., ``The Implementation of POSTGRES,'' IEEE
+ Transactions on Knowledge and Data Engineering 2(1), March 1990.
+
[STON90b]Stonebraker, M. et al., ``On Rules, Procedures, Caching and Views in Database Systems,'' Proc. 1990 ACM-SIGMOD Conference on+ Management of Data, Atlantic City, N.J.,
+ June 1990.
+
+
+
+
+
+
--- /dev/null
+
+
+
The POSTGRES95 User Manual - THE POSTGRES RULE SYSTEM
+
+
+
+
+
+
+
+
14. THE POSTGRES RULE SYSTEM
+
+ Production rule systems are conceptually simple, but
+ there are many subtle points involved in actually using
+ them. Consequently, we will not attempt to explain the
+ actual syntax and operation of the POSTGRES rule system
+ here. Instead, you should read
[STON90b] to understand+ some of these points and the theoretical foundations of
+ the POSTGRES rule system before trying to use rules.
+ The discussion in this section is intended to provide
+ an overview of the POSTGRES rule system and point the
+ user at helpful references and examples.
+ The "query rewrite" rule system modifies queries to
+ take rules into consideration, and then passes the modified
+ query to the query optimizer for execution. It
+ is very powerful, and can be used for many things such
+ as query language procedures, views, and versions. The
+ power of this rule system is discussed in
+
+
+
+
+
+
+
--- /dev/null
+
+
+
The POSTGRES95 User Manual - GETTING STARTED
+
+
+
+
+
+
+
+
3. GETTING STARTED WITH POSTGRES
+
+ This section discusses how to start POSTGRES and set up
+ your own environment so that you can use frontend
+ applications. We assume POSTGRES has already been
+ successfully installed. (Refer to the installation notes
+ for how to install POSTGRES.)
+ Some of the steps listed in this section will apply to
+ all POSTGRES users, and some will apply primarily to
+ the site database administrator. This site administrator
+ is the person who installed the software, created
+ the database directories and started the postmaster
+ process. This person does not have to be the UNIX
+ superuser, "root," or the computer system administrator.
+ In this section, items for end users are labelled
+ "User" and items intended for the site administrator
+ are labelled "Admin."
+ Throughout this manual, any examples that begin with
+ the character ``%'' are commands that should be typed
+ at the UNIX shell prompt. Examples that begin with the
+ character ``*'' are commands in the POSTGRES query
+ language, POSTGRES SQL.
+
+
3.1. Admin/User: Setting Up Your Environment
+ Figure 2. shows how the POSTGRES distribution is laid
+ out when installed in the default way. For simplicity,
+ we will assume that POSTGRES has been installed in the
+ directory /usr/local/postgres95. Therefore, wherever
+ you see the directory /usr/local/postgres95 you should
+ substitute the name of the directory where POSTGRES is
+ actually installed.
+ All POSTGRES commands are installed in the directory
+ /usr/local/postgres95/bin. Therefore, you should add
+ this directory to your shell command path. If you use
+ a variant of the Berkeley C shell, such as csh or tcsh,
+ you would add
+
% set path = ( /usr/local/postgres95/bin $path )
+
+ in the .login file in your home directory. If you use
+ a variant of the Bourne shell, such as sh, ksh, or
+ bash, then you would add
+ % PATH=/usr/local/postgres95/bin:$PATH
+ % export PATH
+
+ to the .profile file in your home directory.
+ From now on, we will assume that you have added the
+ POSTGRES bin directory to your path. In addition, we
+ will make frequent reference to "setting a shell
+ variable" or "setting an environment variable" throughout
+ this document. If you did not fully understand the
+ last paragraph on modifying your search path, you
+ should consult the UNIX manual pages that describe your
+ shell before going any further.
+
+
3.2. Admin: Starting the Postmaster
+ It should be clear from the preceding discussion that
+ nothing can happen to a database unless the postmaster
+ process is running. As the site administrator, there
+ are a number of things you should remember before
+ starting the postmaster. These are discussed in the
+ section of this manual titled, "Administering POSTGRES."
+ However, if POSTGRES has been installed by following
+ the installation instructions exactly as written, the
+ following simple command is all you should
+ need to start the postmaster:
+
+ The postmaster occasionally prints out messages which
+ are often helpful during troubleshooting. If you wish
+ to view debugging messages from the postmaster, you can
+ start it with the -d option and redirect the output to
+ the log file:
+
% postmaster -d >& pm.log &
+
+ If you do not wish to see these messages, you can type
+
+ and the postmaster will be "S"ilent. Notice that there
+ is no ampersand ("&") at the end of the last example.
+
+
3.3. Admin: Adding and Deleting Users
+ The createuser command enables specific users to access
+ POSTGRES. The destroyuser command removes users and
+ prevents them from accessing POSTGRES. Note that these
+ commands only affect users with respect to POSTGRES;
+ they have no effect administration of users that the
+ operating system manages.
+
+
3.4. User: Starting Applications
+ Assuming that your site administrator has properly
+ started the postmaster process and authorized you to
+ use the database, you (as a user) may begin to start up
+ applications. As previously mentioned, you should add
+ /usr/local/postgres95/bin to your shell search path.
+ In most cases, this is all you should have to do in
+ If you get the following error message from a POSTGRES
+ command (such as psql or createdb):
+
connectDB() failed: Is the postmaster running at 'localhost' on port '4322'?
+
+ it is usually because (1) the postmaster is not running, or (2) you are attempting to connect to the wrong
+ server host.
+ If you get the following error message:
+
FATAL 1:Feb 17 23:19:55:process userid (2360) !=
+ database owner (268)
+
+ it means that the site administrator started the postmaster as the wrong user. Tell him to restart it as
+ the POSTGRES superuser.
+
+
3.5. User: Managing a Database
+ Now that POSTGRES is up and running we can create some
+ databases to experiment with. Here, we describe the
+ basic commands for managing a database.
+
+
3.5.1. Creating a Database
+ Let's say you want to create a database named mydb.
+ You can do this with the following command:
+
+
+ POSTGRES allows you to create any number of databases
+ at a given site and you automatically become the
+ database administrator of the database you just created. Database names must have an alphabetic first
+ character and are limited to 16 characters in length.
+ Not every user has authorization to become a database
+ administrator. If POSTGRES refuses to create databases
+ for you, then the site administrator needs to grant you
+ permission to create databases. Consult your site
+ administrator if this occurs.
+
+
3.5.2. Accessing a Database
+ Once you have constructed a database, you can access it
+ by:
+
running the POSTGRES terminal monitor programs (
+ monitor or psql) which allows you to interactively
+ enter, edit, and execute SQL commands.
+
writing a C program using the LIBPQ subroutine
+ library. This allows you to submit SQL commands
+ from C and get answers and status messages back to
+ your program. This interface is discussed further
+ in section ??.
+
+ You might want to start up psql, to try out the examples in this manual. It can be activated for the mydb
+ database by typing the command:
+
+ You will be greeted with the following message:
+
Welcome to the POSTGRES95 interactive sql monitor:
+
+ type \? for help on slash commands
+ type \q to quit
+ type \g or terminate with semicolon to execute query
+ You are currently connected to the database: mydb
+
+ mydb=>
+ This prompt indicates that the terminal monitor is listening to you and that you can type SQL queries into a
+ workspace maintained by the terminal monitor.
+ The psql program responds to escape codes that begin
+ with the backslash character, "\". For example, you
+ can get help on the syntax of various POSTGRES SQL commands by typing:
+
+ Once you have finished entering your queries into the
+ workspace, you can pass the contents of the workspace
+ to the POSTGRES server by typing:
+
+ This tells the server to process the query. If you
+ terminate your query with a semicolon, the \g is not
+ necessary. psql will automatically process semicolon terminated queries.
+ To read queries from a file, say myFile, instead of
+ entering them interactively, type:
+
+ To get out of psql and return to UNIX, type
+
+ and psql will quit and return you to your command
+ shell. (For more escape codes, type \h at the monitor
+ prompt.)
+ White space (i.e., spaces, tabs and newlines) may be
+ used freely in SQL queries. Comments are denoted by
+ --. Everything after the dashes up to the end of the
+ line is ignored.
+
+
3.5.3. Destroying a Database
+ If you are the database administrator for the database
+ mydb, you can destroy it using the following UNIX command:
+
+ This action physically removes all of the UNIX files
+ associated with the database and cannot be undone, so
+ this should only be done with a great deal of fore-thought.
+
+
+
+
1. If your site administrator has not set things up in the+default way, you may have some more work to do. For example, if the database server machine is a remote machine, you
+will need to set the PGHOST environment variable to the name
+of the database server machine. The environment variable
+PGPORT may also have to be set. The bottom line is this: if
+you try to start an application program and it complains
+that it cannot connect to the postmaster, you should immediately consult your site administrator to make sure that your
+environment is properly set up.
+
+
+
+
+
+
--- /dev/null
+
+
+
The POSTGRES95 User Manual - EXTENDING SQL: AGGREGATES
+
+
+
+
+
+
+
+
10. EXTENDING SQL: AGGREGATES
+
+ Aggregates in POSTGRES are expressed in terms of state
+ transition functions. That is, an aggregate can be
+ defined in terms of state that is modified whenever an
+ instance is processed. Some state functions look at a
+ particular value in the instance when computing the new
+ state (sfunc1 in the create aggregate syntax) while
+ others only keep track of their own internal state
+ (sfunc2).
+ If we define an aggregate that uses only sfunc1, we
+ define an aggregate that computes a running function of
+ the attribute values from each instance. "Sum" is an
+ example of this kind of aggregate. "Sum" starts at
+ zero and always adds the current instance's value to
+ its running total. We will use the int4pl that is
+ built into POSTGRES to perform this addition.
+
+
CREATE AGGREGATE complex_sum (
+ sfunc1 = complex_add,
+ basetype = complex,
+ stype1 = complex,
+ initcond1 = '(0,0)'
+ );
+
+
+ SELECT complex_sum(a) FROM test_complex;
+
+
+ +------------+
+ |complex_sum |
+ +------------+
+ |(34,53.9) |
+ +------------+
+
+
+ If we define only sfunc2, we are specifying an aggregate
+ that computes a running function that is independent of
+ the attribute values from each instance.
+ "Count" is the most common example of this kind of
+ aggregate. "Count" starts at zero and adds one to its
+ running total for each instance, ignoring the instance
+ value. Here, we use the built-in int4inc routine to do
+ the work for us. This routine increments (adds one to)
+ its argument.
+
+
CREATE AGGREGATE my_count (sfunc2 = int4inc, -- add one
+ basetype = int4, stype2 = int4,
+ initcond2 = '0')
+
+ SELECT my_count(*) as emp_count from EMP;
+
+
+ +----------+
+ |emp_count |
+ +----------+
+ |5 |
+ +----------+
+
+
+ "Average" is an example of an aggregate that requires
+ both a function to compute the running sum and a function
+ to compute the running count. When all of the
+ instances have been processed, the final answer for the
+ aggregate is the running sum divided by the running
+ count. We use the int4pl and int4inc routines we used
+ before as well as the POSTGRES integer division
+ routine, int4div, to compute the division of the sum by
+ the count.
+
+
CREATE AGGREGATE my_average (sfunc1 = int4pl, -- sum
+ basetype = int4,
+ stype1 = int4,
+ sfunc2 = int4inc, -- count
+ stype2 = int4,
+ finalfunc = int4div, -- division
+ initcond1 = '0',
+ initcond2 = '0')
+
+ SELECT my_average(salary) as emp_average FROM EMP;
+
+
+ +------------+
+ |emp_average |
+ +------------+
+ |1640 |
+ +------------+
+
+
+
+
+
+
--- /dev/null
+
+
+
The POSTGRES95 User Manual - EXTENDING SQL: FUNCTIONS
+
+
+
+
+
+
+
+
7. EXTENDING SQL: FUNCTIONS
+
+ As it turns out, part of defining a new type is the
+ definition of functions that describe its behavior.
+ Consequently, while it is possible to define a new
+ function without defining a new type, the reverse is
+ not true. We therefore describe how to add new functions
+ to POSTGRES before describing how to add new
+ types.
+ POSTGRES SQL provides two types of functions: query
+ language functions (functions written in SQL and
+ programming language functions (functions written in a
+ compiled programming language such as C.) Either kind
+ of function can take a base type, a composite type or
+ some combination as arguments (parameters). In addition,
+ both kinds of functions can return a base type or
+ a composite type. It's easier to define SQL functions,
+ so we'll start with those.
+ Examples in this section can also be found in funcs.sql
+ and C-code/funcs.c.
+
7.1. Query Language (SQL) Functions
+
+
7.1.1. SQL Functions on Base Types
+ The simplest possible SQL function has no arguments and
+ simply returns a base type, such as int4:
+
+
CREATE FUNCTION one() RETURNS int4
+ AS 'SELECT 1 as RESULT' LANGUAGE 'sql';
+
+
+ SELECT one() AS answer;
+
+ +-------+
+ |answer |
+ +-------+
+ |1 |
+ +-------+
+
+ Notice that we defined a target list for the function
+ (with the name RESULT), but the target list of the
+ query that invoked the function overrode the function's
+ target list. Hence, the result is labelled answer
+ instead of one.
+ It's almost as easy to define SQL functions that take
+ base types as arguments. In the example below, notice
+ how we refer to the arguments within the function as $1
+ and $2.
+
+
CREATE FUNCTION add_em(int4, int4) RETURNS int4
+ AS 'SELECT $1 + $2;' LANGUAGE 'sql';
+
+
+ SELECT add_em(1, 2) AS answer;
+
+
+ +-------+
+ |answer |
+ +-------+
+ |3 |
+ +-------+
+
+
+
7.1.2. SQL Functions on Composite Types
+ When specifying functions with arguments of composite
+ types (such as EMP), we must not only specify which
+ argument we want (as we did above with $1 and $2) but
+ also the attributes of that argument. For example,
+ take the function double_salary that computes what your
+ salary would be if it were doubled.
+
+
CREATE FUNCTION double_salary(EMP) RETURNS int4
+ AS 'SELECT $1.salary * 2 AS salary;' LANGUAGE 'sql';
+
+ SELECT name, double_salary(EMP) AS dream
+ FROM EMP
+ WHERE EMP.dept = 'toy';
+
+
+ +-----+-------+
+ |name | dream |
+ +-----+-------+
+ |Sam | 2400 |
+ +-----+-------+
+
+ Notice the use of the syntax $1.salary.
+ Before launching into the subject of functions that
+ return composite types, we must first introduce the
+ function notation for projecting attributes. The simple way
+ to explain this is that we can usually use the
+ notation attribute(class) and class.attribute interchangably.
+
+ -- this is the same as:
+ -- SELECT EMP.name AS youngster FROM EMP WHERE EMP.age < 30
+ --
+ SELECT name(EMP) AS youngster
+ FROM EMP
+ WHERE age(EMP) < 30;
+
+
+ +----------+
+ |youngster |
+ +----------+
+ |Sam |
+ +----------+
+
+ As we shall see, however, this is not always the case.
+ This function notation is important when we want to use
+ a function that returns a single instance. We do this
+ by assembling the entire instance within the function,
+ attribute by attribute. This is an example of a function
+ that returns a single EMP instance:
+
+
CREATE FUNCTION new_emp() RETURNS EMP
+ AS 'SELECT \'None\'::text AS name,
+ 1000 AS salary,
+ 25 AS age,
+ \'none\'::char16 AS dept;'
+ LANGUAGE 'sql';
+
+
+ In this case we have specified each of the attributes
+ with a constant value, but any computation or expression
+ could have been substituted for these constants.
+ Defining a function like this can be tricky. Some of
+ the more important caveats are as follows:
+
+
+
The target list order must be exactly the same as
+ that in which the attributes appear in the CREATE
+ TABLE statement (or when you execute a .* query).
+
You must be careful to typecast the expressions
+ (using ::) very carefully or you will see the following error:
+
+
WARN::function declared to return type EMP does not retrieve (EMP.*)
+
+
When calling a function that returns an instance, we
+ cannot retrieve the entire instance. We must either
+ project an attribute out of the instance or pass the
+ entire instance into another function.
+
SELECT name(new_emp()) AS nobody;
+
+
+ +-------+
+ |nobody |
+ +-------+
+ |None |
+ +-------+
+
+
The reason why, in general, we must use the function
+ syntax for projecting attributes of function return
+ values is that the parser just doesn't understand
+ the other (dot) syntax for projection when combined
+ with function calls.
+
+
SELECT new_emp().name AS nobody;
+ WARN:parser: syntax error at or near "."
+
+
+
+ Any collection of commands in the SQL query language
+ can be packaged together and defined as a function.
+ The commands can include updates (i.e., insert, update
+ and delete) as well as select queries. However, the
+ final command must be a select that returns whatever is
+ specified as the function's returntype.
+
+ CREATE FUNCTION clean_EMP () RETURNS int4
+ AS 'DELETE FROM EMP WHERE EMP.salary <= 0;
+ SELECT 1 AS ignore_this'
+ LANGUAGE 'sql';
+
+ SELECT clean_EMP();
+
+
+ +--+
+ |x |
+ +--+
+ |1 |
+ +--+
+
+
+
7.2. Programming Language Functions
+
7.2.1. Programming Language Functions on Base Types
+ Internally, POSTGRES regards a base type as a "blob of
+ memory." The user-defined functions that you define
+ over a type in turn define the way that POSTGRES can
+ operate on it. That is, POSTGRES will only store and
+ retrieve the data from disk and use your user-defined
+ functions to input, process, and output the data.
+ Base types can have one of three internal formats:
+
pass by value, fixed-length
+
pass by reference, fixed-length
+
pass by reference, variable-length
+
+ By-value types can only be 1, 2 or 4 bytes in length
+ (even if your computer supports by-value types of other
+ sizes). POSTGRES itself only passes integer types by
+ value. You should be careful to define your types such
+ that they will be the same size (in bytes) on all
+ architectures. For example, the long type is dangerous
+ because it is 4 bytes on some machines and 8 bytes on
+ others, whereas int type is 4 bytes on most UNIX
+ machines (though not on most personal computers). A
+ reasonable implementation of the int4 type on UNIX
+ machines might be:
+
+
/* 4-byte integer, passed by value */
+ typedef int int4;
+
+
+ On the other hand, fixed-length types of any size may
+ be passed by-reference. For example, here is a sample
+ implementation of the POSTGRES char16 type:
+
+
/* 16-byte structure, passed by reference */
+ typedef struct {
+ char data[16];
+ } char16;
+
+
+ Only pointers to such types can be used when passing
+ them in and out of POSTGRES functions.
+ Finally, all variable-length types must also be passed
+ by reference. All variable-length types must begin
+ with a length field of exactly 4 bytes, and all data to
+ be stored within that type must be located in the memory
+ immediately following that length field. The
+ length field is the total length of the structure
+ (i.e., it includes the size of the length field
+ itself). We can define the text type as follows:
+
+ int4 length;
+ char data[1];
+ } text;
+
+
+ Obviously, the data field is not long enough to hold
+ all possible strings -- it's impossible to declare such
+ a structure in C. When manipulating variable-length
+ types, we must be careful to allocate the correct
+ amount of memory and initialize the length field. For
+ example, if we wanted to store 40 bytes in a text
+ structure, we might use a code fragment like this:
+
+ #include "utils/palloc.h"
+
+ ...
+
+ char buffer[40]; /* our source data */
+
+ ...
+
+ text *destination = (text *) palloc(VARHDRSZ + 40);
+ destination->length = VARHDRSZ + 40;
+ memmove(destination->data, buffer, 40);
+
+ ...
+
+
+ Now that we've gone over all of the possible structures
+ for base types, we can show some examples of real functions.
+ Suppose funcs.c look like:
+
+ #include "postgres.h" /* for char16, etc. */
+ #include "utils/palloc.h" /* for palloc */
+
+ int
+ add_one(int arg)
+ {
+ return(arg + 1);
+ }
+
+ char16 *
+ concat16(char16 *arg1, char16 *arg2)
+ {
+ char16 *new_c16 = (char16 *) palloc(sizeof(char16));
+
+ memset((void *) new_c16, 0, sizeof(char16));
+ (void) strncpy(new_c16, arg1, 16);
+ return (char16 *)(strncat(new_c16, arg2, 16));
+ }
+ text *
+ copytext(text *t)
+ {
+ /*
+ * VARSIZE is the total size of the struct in bytes.
+ */
+ text *new_t = (text *) palloc(VARSIZE(t));
+ memset(new_t, 0, VARSIZE(t));
+ VARSIZE(new_t) = VARSIZE(t);
+ /*
+ * VARDATA is a pointer to the data region of the struct.
+ */
+ memcpy((void *) VARDATA(new_t), /* destination */
+ (void *) VARDATA(t), /* source */
+ VARSIZE(t)-VARHDRSZ); /* how many bytes */
+ return(new_t);
+ }
+
+ On OSF/1 we would type:
+
+
CREATE FUNCTION add_one(int4) RETURNS int4
+ AS '/usr/local/postgres95/tutorial/obj/funcs.so' LANGUAGE 'c';
+
+ CREATE FUNCTION concat16(char16, char16) RETURNS char16
+ AS '/usr/local/postgres95/tutorial/obj/funcs.so' LANGUAGE 'c';
+
+ CREATE FUNCTION copytext(text) RETURNS text
+ AS '/usr/local/postgres95/tutorial/obj/funcs.so' LANGUAGE 'c';
+
+
+ On other systems, we might have to make the filename
+ end in .sl (to indicate that it's a shared library).
+
7.2.2. Programming Language Functions on Composite Types
+ Composite types do not have a fixed layout like C
+ structures. Instances of a composite type may contain
+ null fields. In addition, composite types that are
+ part of an inheritance hierarchy may have different
+ fields than other members of the same inheritance hierarchy.
+ Therefore, POSTGRES provides a procedural
+ interface for accessing fields of composite types from
+ C.
+ As POSTGRES processes a set of instances, each instance
+ will be passed into your function as an opaque structure of type TUPLE.
+ Suppose we want to write a function to answer the query
+
+
* SELECT name, c_overpaid(EMP, 1500) AS overpaid
+ FROM EMP
+ WHERE name = 'Bill' or name = 'Sam';
+
+ In the query above, we can define c_overpaid as:
+
+
#include "postgres.h" /* for char16, etc. */
+ #include "libpq-fe.h" /* for TUPLE */
+ bool
+ c_overpaid(TUPLE t,/* the current instance of EMP */
+ int4 limit)
+ {
+ bool isnull = false;
+ int4 salary;
+ salary = (int4) GetAttributeByName(t, "salary", &isnull);
+ if (isnull)
+ return (false);
+ return(salary > limit);
+ }
+
+
+ GetAttributeByName is the POSTGRES system function that
+ returns attributes out of the current instance. It has
+ three arguments: the argument of type TUPLE passed into
+ the function, the name of the desired attribute, and a
+ return parameter that describes whether the attribute
+ is null. GetAttributeByName will align data properly
+ so you can cast its return value to the desired type.
+ For example, if you have an attribute name which is of
+ the type char16, the GetAttributeByName call would look
+ like:
+
+ ...
+ str = (char *) GetAttributeByName(t, "name", &isnull)
+
+
+ The following query lets POSTGRES know about the
+ c_overpaid function:
+
+
* CREATE FUNCTION c_overpaid(EMP, int4) RETURNS bool
+ AS '/usr/local/postgres95/tutorial/obj/funcs.so' LANGUAGE 'c';
+
+ While there are ways to construct new instances or modify
+ existing instances from within a C function, these
+ are far too complex to discuss in this manual.
+ We now turn to the more difficult task of writing
+ programming language functions. Be warned: this section
+ of the manual will not make you a programmer. You must
+ have a good understanding of C (including the use of
+ pointers and the malloc memory manager) before trying
+ to write C functions for use with POSTGRES.
+ While it may be possible to load functions written in
+ languages other than C into POSTGRES, this is often
+ difficult (when it is possible at all) because other
+ languages, such as FORTRAN and Pascal often do not follow
+ the same "calling convention" as C. That is, other
+ languages do not pass argument and return values
+ between functions in the same way. For this reason, we
+ will assume that your programming language functions
+ are written in C.
+ The basic rules for building C functions are as follows:
+
Most of the header (include) files for POSTGRES
+ should already be installed in
+ /usr/local/postgres95/include (see Figure 2).
+ You should always include
+
+
-I/usr/local/postgres95/include
+
+ on your cc command lines. Sometimes, you may
+ find that you require header files that are in
+ the server source itself (i.e., you need a file
+ we neglected to install in include). In those
+ cases you may need to add one or more of
+ -I/usr/local/postgres95/src/backend
+ -I/usr/local/postgres95/src/backend/include
+ -I/usr/local/postgres95/src/backend/port/<PORTNAME>
+ -I/usr/local/postgres95/src/backend/obj
+
+
+ (where <PORTNAME> is the name of the port, e.g.,
+ alpha or sparc).
+
When allocating memory, use the POSTGRES
+ routines palloc and pfree instead of the
+ corresponding C library routines malloc and free.
+ The memory allocated by palloc will be freed
+ automatically at the end of each transaction,
+ preventing memory leaks.
+
Always zero the bytes of your structures using
+ memset or bzero. Several routines (such as the
+ hash access method, hash join and the sort algorithm)
+ compute functions of the raw bits contained in
+ your structure. Even if you initialize all fields
+ of your structure, there may be
+ several bytes of alignment padding (holes in the
+ structure) that may contain garbage values.
+
Most of the internal POSTGRES types are declared
+ in postgres.h, so it's usually a good idea to
+ include that file as well.
+
Compiling and loading your object code so that
+ it can be dynamically loaded into POSTGRES
+ always requires special flags. See Appendix A
+ for a detailed explanation of how to do it for
+ your particular operating system.
+
+
+
+
+
+
--- /dev/null
+
+
+
The POSTGRES95 User Manual - THE QUERY LANGUAGE
+
+
+
+
+
+
+
+
11. INTERFACING EXTENSIONS TO INDICES
+
+ The procedures described thus far let you define a new
+ type, new functions and new operators. However, we
+ cannot yet define a secondary index (such as a B-tree,
+ R-tree or hash access method) over a new type or its
+
+ The right half shows the catalogs
+ that we must modify in order to tell POSTGRES how
+ to use a user-defined type and/or user-defined operators
+ with an index (i.e., pg_am, pg_amop, pg_amproc and
+ pg_opclass). Unfortunately, there is no simple command
+ to do this. We will demonstrate how to modify these
+ catalogs through a running example: a new operator
+ class for the B-tree access method that sorts integers
+ in ascending absolute value order.
+
+ The pg_am class contains one instance for every user
+ defined access method. Support for the heap access
+ method is built into POSTGRES, but every other access
+ method is described here. The schema is
+
+
+
amname | name of the access method |
+
+
amowner | object id of the owner's instance in pg_user |
+
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