int2
The total number of columns in the index (duplicates
- pg_class.relnatts). This number includes both key and included attributes.
+ pg_class.relnatts); this number includes both key and included attributes
|
indnkeyatts
int2
- The number of key columns in the index. "Key columns" are ordinary
- index columns (as opposed to "included" columns).
+ The number of key columns in the index,
+ not counting any included columns, which are
+ merely stored and do not participate in the index semantics
|
This is an array of indnatts values that
indicate which table columns this index indexes. For example a value
of 1 3 would mean that the first and the third table
- columns make up the index key. A zero in this array indicates that the
+ columns make up the index entries. Key columns come before non-key
+ (included) columns. A zero in this array indicates that the
corresponding index attribute is an expression over the table columns,
rather than a simple column reference.
oidvector
pg_collation.oid
- For each column in the index key, this contains the OID of the
- collation to use for the index, or zero if the column is not
- of a collatable data type.
+ For each column in the index key
+ (indnkeyatts values), this contains the OID
+ of the collation to use for the index, or zero if the column is not of
+ a collatable data type.
oidvector
pg_opclass.oid
- For each column in the index key, this contains the OID of
- the operator class to use. See
+ For each column in the index key
+ (indnkeyatts values), this contains the OID
+ of the operator class to use. See
pg_opclass for details.
int2vector
- This is an array of indnatts values that
+ This is an array of indnkeyatts values that
store per-column flag bits. The meaning of the bits is defined by
the index's access method.
bool ampredlocks;
/* does AM support parallel scan? */
bool amcanparallel;
- /* type of data stored in index, or InvalidOid if variable */
- Oid amkeytype;
/* does AM support columns included with clause INCLUDE? */
bool amcaninclude;
+ /* type of data stored in index, or InvalidOid if variable */
+ Oid amkeytype;
/* interface functions */
ambuild_function ambuild;
using unique indexes, which are indexes that disallow
multiple entries with identical keys. An access method that supports this
feature sets amcanunique true.
- (At present, only b-tree supports it.) Columns listed in the
- INCLUDE clause are not used to enforce uniqueness.
+ (At present, only b-tree supports it.) Columns listed in the
+ INCLUDE clause are not considered when enforcing
+ uniqueness.
or the uniqueness of the combined values of more than one column.
CREATE UNIQUE INDEX name ON table (column , ...)
-[ INCLUDE (column , ...) ];
+ INCLUDE (column , ...) ;
Currently, only B-tree indexes can be declared unique.
When an index is declared unique, multiple table rows with equal
indexed values are not allowed. Null values are not considered
equal. A multicolumn unique index will only reject cases where all
- indexed columns are equal in multiple rows. Columns listed in the
- INCLUDE clause aren't used to enforce constraints
- (UNIQUE, PRIMARY KEY, etc).
+ indexed columns are equal. Columns listed in
+ the INCLUDE clause, if any, aren't considered when
+ determining whether index entries are equal.
The optional INCLUDE clause specifies a
- list of columns which will be included as a non-key part in the index.
- Columns listed in this clause cannot also be present as index key columns.
- The INCLUDE columns exist solely to
- allow more queries to benefit from index-only scans
- by including the values of the specified columns in the index. These values
- would otherwise have to be obtained by reading the table's heap.
+ list of columns which will be included in the index
+ as non-key columns. A non-key column cannot
+ be used in an index scan search qualification, and it is disregarded
+ for purposes of any uniqueness or exclusion constraint enforced by
+ the index. However, an index-only scan can return the contents of
+ non-key columns without having to visit the index's table, since
+ they are available directly from the index entry. Thus, addition of
+ non-key columns allows index-only scans to be used for queries that
+ otherwise could not use them.
- In UNIQUE indexes, uniqueness is only enforced
- for key columns. Columns listed in the INCLUDE
- clause have no effect on uniqueness enforcement. Other constraints
- (PRIMARY KEY and EXCLUDE) work
- the same way.
+ It's wise to be conservative about adding non-key columns to an
+ index, especially wide columns. If an index tuple exceeds the
+ maximum size allowed for the index type, data insertion will fail.
+ In any case, non-key columns duplicate data from the index's table
+ and bloat the size of the index, thus potentially slowing searches.
Columns listed in the INCLUDE clause don't need
- appropriate operator classes; the clause can contain non-key index
+ appropriate operator classes; the clause can include
columns whose data types don't have operator classes defined for
a given access method.
Currently, only the B-tree index access method supports this feature.
In B-tree indexes, the values of columns listed in the
INCLUDE clause are included in leaf tuples which
- are linked to the heap tuples, but are not included into pivot tuples
- used for tree navigation. Therefore, moving columns from the list of
- key columns to the INCLUDE clause can slightly
- reduce index size and improve the tree branching factor.
-
-
- Indexes with columns listed in the INCLUDE clause
- are also called covering indexes
.
+ correspond to heap tuples, but are not included in upper-level
+ index entries used for tree navigation.
columns is updated and so the recheck is not worth the additional cost
of executing the function.
-
+
Functional indexes are used frequently for the case where the function
returns a subset of the argument. Examples of this would be accessing
To create a unique B-tree index on the column title
- and included columns director and rating
- in the table films:
+ with included columns director
+ and rating in the table films:
CREATE UNIQUE INDEX title_idx ON films (title) INCLUDE (director, rating);
one or more columns on which the uniqueness is not enforced.
Note that although the constraint is not enforced on the included columns,
it still depends on them. Consequently, some operations on these columns
- (e.g. DROP COLUMN) can cause cascade constraint and
- index deletion. See paragraph about INCLUDE in
- for more information.
+ (e.g. DROP COLUMN) can cause cascaded constraint and
+ index deletion.
of columns to be specified which will be included in the non-key portion
of the index. Although uniqueness is not enforced on the included columns,
the constraint still depends on them. Consequently, some operations on the
- included columns (e.g. DROP COLUMN) can cause cascade
- constraint and index deletion. See paragraph about INCLUDE
- in for more information.
+ included columns (e.g. DROP COLUMN) can cause cascaded
+ constraint and index deletion.
Snapshot snapshot;
int i;
- if (list_intersection(stmt->indexParams, stmt->indexIncludingParams) != NIL)
- ereport(ERROR,
- (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
- errmsg("included columns must not intersect with key columns")));
-
/*
* count key attributes in index
*/
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("access method \"%s\" does not support unique indexes",
accessMethodName)));
- if (list_length(stmt->indexIncludingParams) > 0 && !amRoutine->amcaninclude)
+ if (stmt->indexIncludingParams != NIL && !amRoutine->amcaninclude)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("access method \"%s\" does not support included columns",
-- Regular index with included columns
CREATE TABLE tbl_include_reg (c1 int, c2 int, c3 int, c4 box);
INSERT INTO tbl_include_reg SELECT x, 2*x, 3*x, box('4,4,4,4') FROM generate_series(1,10) AS x;
-CREATE INDEX tbl_include_reg_idx ON tbl_include_reg using btree (c1, c2) INCLUDE (c3,c4);
--- must fail because of intersection of key and included columns
-CREATE INDEX tbl_include_reg_idx ON tbl_include_reg using btree (c1, c2) INCLUDE (c1,c3);
-ERROR: included columns must not intersect with key columns
+CREATE INDEX tbl_include_reg_idx ON tbl_include_reg (c1, c2) INCLUDE (c3, c4);
+-- duplicate column is pretty pointless, but we allow it anyway
+CREATE INDEX ON tbl_include_reg (c1, c2) INCLUDE (c1, c3);
SELECT pg_get_indexdef(i.indexrelid)
FROM pg_index i JOIN pg_class c ON i.indexrelid = c.oid
WHERE i.indrelid = 'tbl_include_reg'::regclass ORDER BY c.relname;
- pg_get_indexdef
---------------------------------------------------------------------------------------------------
+ pg_get_indexdef
+---------------------------------------------------------------------------------------------------------------
+ CREATE INDEX tbl_include_reg_c1_c2_c11_c3_idx ON public.tbl_include_reg USING btree (c1, c2) INCLUDE (c1, c3)
CREATE INDEX tbl_include_reg_idx ON public.tbl_include_reg USING btree (c1, c2) INCLUDE (c3, c4)
-(1 row)
+(2 rows)
-- Unique index and unique constraint
CREATE TABLE tbl_include_unique1 (c1 int, c2 int, c3 int, c4 box);
-- Regular index with included columns
CREATE TABLE tbl_include_reg (c1 int, c2 int, c3 int, c4 box);
INSERT INTO tbl_include_reg SELECT x, 2*x, 3*x, box('4,4,4,4') FROM generate_series(1,10) AS x;
-CREATE INDEX tbl_include_reg_idx ON tbl_include_reg using btree (c1, c2) INCLUDE (c3,c4);
--- must fail because of intersection of key and included columns
-CREATE INDEX tbl_include_reg_idx ON tbl_include_reg using btree (c1, c2) INCLUDE (c1,c3);
+CREATE INDEX tbl_include_reg_idx ON tbl_include_reg (c1, c2) INCLUDE (c3, c4);
+-- duplicate column is pretty pointless, but we allow it anyway
+CREATE INDEX ON tbl_include_reg (c1, c2) INCLUDE (c1, c3);
SELECT pg_get_indexdef(i.indexrelid)
FROM pg_index i JOIN pg_class c ON i.indexrelid = c.oid
WHERE i.indrelid = 'tbl_include_reg'::regclass ORDER BY c.relname;
projects / postgresql.git / commitdiff