Fix several DDL issues of generated columns versus inheritance

Several combinations of generated columns and inheritance in CREATE
TABLE were not handled correctly.  Specifically:

- Disallow a child column specifying a generation expression if the
  parent column is a generated column.  The child column definition
  must be unadorned and the parent column's generation expression will
  be copied.

- Prohibit a child column of a generated parent column specifying
  default values or identity.

- Allow a child column of a not-generated parent column specifying
  itself as a generated column.  This previously did not work, but it
  was possible to arrive at the state via other means (involving ALTER
  TABLE), so it seems sensible to support it.

Add tests for each case.  Also add documentation about the rules
involving generated columns and inheritance.

Discussion:
    https://www.postgresql.org/message-id/flat/15830.1575468847%40sss.pgh.pa.us
    https://www.postgresql.org/message-id/flat/2678bad1-048f-519a-ef24-b12962f41807%40enterprisedb.com
    https://www.postgresql.org/message-id/flat/CAJvUf_u4h0DxkCMCeEKAWCuzGUTnDP-G5iVmSwxLQSXn0_FWNQ%40mail.gmail.com

diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index a20e5fb366d11917c4454b3c90e37aa3ff2f2af2..bf9f0181eab64b0d67ae085c41383aac6042f8cd 100644 (file)
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -324,6 +324,32 @@ CREATE TABLE people (
       linkend="sql-createforeigntable"/> for details.
      
     
+    
+     For inheritance:
+     
+      
+       
+        If a parent column is a generated column, a child column must also be
+        a generated column using the same expression.  In the definition of
+        the child column, leave off the GENERATED clause,
+        as it will be copied from the parent.
+       
+      
+      
+       
+        In case of multiple inheritance, if one parent column is a generated
+        column, then all parent columns must be generated columns and with the
+        same expression.
+       
+      
+      
+       
+        If a parent column is not a generated column, a child column may be
+        defined to be a generated column or not.
+       
+      
+     
+    
    
   
 

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index b36683e74974dba4e75a85eda729fe2f9cde586e..2a15e07ede70be08245dc95545913a417a9ae35d 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -2577,12 +2577,55 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
                def->is_local = true;
                /* Merge of NOT NULL constraints = OR 'em together */
                def->is_not_null |= newdef->is_not_null;
+
+               /*
+                * Check for conflicts related to generated columns.
+                *
+                * If the parent column is generated, the child column must be
+                * unadorned and will be made a generated column.  (We could
+                * in theory allow the child column definition specifying the
+                * exact same generation expression, but that's a bit
+                * complicated to implement and doesn't seem very useful.)  We
+                * also check that the child column doesn't specify a default
+                * value or identity, which matches the rules for a single
+                * column in parse_util.c.
+                */
+               if (def->generated)
+               {
+                   if (newdef->generated)
+                       ereport(ERROR,
+                               (errcode(ERRCODE_INVALID_COLUMN_DEFINITION),
+                                errmsg("child column \"%s\" specifies generation expression",
+                                       def->colname),
+                                errhint("Omit the generation expression in the definition of the child table column to inherit the generation expression from the parent table.")));
+                   if (newdef->raw_default && !newdef->generated)
+                       ereport(ERROR,
+                               (errcode(ERRCODE_INVALID_COLUMN_DEFINITION),
+                                errmsg("column \"%s\" inherits from generated column but specifies default",
+                                       def->colname)));
+                   if (newdef->identity)
+                       ereport(ERROR,
+                               (errcode(ERRCODE_INVALID_COLUMN_DEFINITION),
+                                errmsg("column \"%s\" inherits from generated column but specifies identity",
+                                       def->colname)));
+               }
+               /*
+                * If the parent column is not generated, then take whatever
+                * the child column definition says.
+                */
+               else
+               {
+                   if (newdef->generated)
+                       def->generated = newdef->generated;
+               }
+
                /* If new def has a default, override previous default */
                if (newdef->raw_default != NULL)
                {
                    def->raw_default = newdef->raw_default;
                    def->cooked_default = newdef->cooked_default;
                }
+
            }
            else
            {
@@ -2668,11 +2711,19 @@ MergeAttributes(List *schema, List *supers, char relpersistence,
            ColumnDef  *def = lfirst(entry);
 
            if (def->cooked_default == &bogus_marker)
-               ereport(ERROR,
-                       (errcode(ERRCODE_INVALID_COLUMN_DEFINITION),
-                        errmsg("column \"%s\" inherits conflicting default values",
-                               def->colname),
-                        errhint("To resolve the conflict, specify a default explicitly.")));
+           {
+               if (def->generated)
+                   ereport(ERROR,
+                           (errcode(ERRCODE_INVALID_COLUMN_DEFINITION),
+                            errmsg("column \"%s\" inherits conflicting generation expressions",
+                                   def->colname)));
+               else
+                   ereport(ERROR,
+                           (errcode(ERRCODE_INVALID_COLUMN_DEFINITION),
+                            errmsg("column \"%s\" inherits conflicting default values",
+                                   def->colname),
+                            errhint("To resolve the conflict, specify a default explicitly.")));
+           }
        }
    }
 

diff --git a/src/test/regress/expected/generated.out b/src/test/regress/expected/generated.out
index f87c86a8ced0c978077bfb96f4a2ecd813d868d2..cea278a89a94727deea82f48cf772ed2632a4551 100644 (file)
--- a/src/test/regress/expected/generated.out
+++ b/src/test/regress/expected/generated.out
@@ -219,12 +219,54 @@ SELECT * FROM gtest1;
  4 | 8
 (2 rows)
 
--- test inheritance mismatch
+CREATE TABLE gtest_normal (a int, b int);
+CREATE TABLE gtest_normal_child (a int, b int GENERATED ALWAYS AS (a * 2) STORED) INHERITS (gtest_normal);
+NOTICE:  merging column "a" with inherited definition
+NOTICE:  merging column "b" with inherited definition
+\d gtest_normal_child
+                      Table "public.gtest_normal_child"
+ Column |  Type   | Collation | Nullable |              Default               
+--------+---------+-----------+----------+------------------------------------
+ a      | integer |           |          | 
+ b      | integer |           |          | generated always as (a * 2) stored
+Inherits: gtest_normal
+
+INSERT INTO gtest_normal (a) VALUES (1);
+INSERT INTO gtest_normal_child (a) VALUES (2);
+SELECT * FROM gtest_normal;
+ a | b 
+---+---
+ 1 |  
+ 2 | 4
+(2 rows)
+
+-- test inheritance mismatches between parent and child
+CREATE TABLE gtestx (x int, b int GENERATED ALWAYS AS (a * 22) STORED) INHERITS (gtest1);  -- error
+NOTICE:  merging column "b" with inherited definition
+ERROR:  child column "b" specifies generation expression
+HINT:  Omit the generation expression in the definition of the child table column to inherit the generation expression from the parent table.
+CREATE TABLE gtestx (x int, b int DEFAULT 10) INHERITS (gtest1);  -- error
+NOTICE:  merging column "b" with inherited definition
+ERROR:  column "b" inherits from generated column but specifies default
+CREATE TABLE gtestx (x int, b int GENERATED ALWAYS AS IDENTITY) INHERITS (gtest1);  -- error
+NOTICE:  merging column "b" with inherited definition
+ERROR:  column "b" inherits from generated column but specifies identity
+-- test multiple inheritance mismatches
 CREATE TABLE gtesty (x int, b int);
 CREATE TABLE gtest1_2 () INHERITS (gtest1, gtesty);  -- error
 NOTICE:  merging multiple inherited definitions of column "b"
 ERROR:  inherited column "b" has a generation conflict
 DROP TABLE gtesty;
+CREATE TABLE gtesty (x int, b int GENERATED ALWAYS AS (x * 22) STORED);
+CREATE TABLE gtest1_2 () INHERITS (gtest1, gtesty);  -- error
+NOTICE:  merging multiple inherited definitions of column "b"
+ERROR:  column "b" inherits conflicting generation expressions
+DROP TABLE gtesty;
+CREATE TABLE gtesty (x int, b int DEFAULT 55);
+CREATE TABLE gtest1_2 () INHERITS (gtest0, gtesty);  -- error
+NOTICE:  merging multiple inherited definitions of column "b"
+ERROR:  inherited column "b" has a generation conflict
+DROP TABLE gtesty;
 -- test stored update
 CREATE TABLE gtest3 (a int, b int GENERATED ALWAYS AS (a * 3) STORED);
 INSERT INTO gtest3 (a) VALUES (1), (2), (3), (NULL);

diff --git a/src/test/regress/sql/generated.sql b/src/test/regress/sql/generated.sql
index bdcedbb9914bd699a7f5e8307bf264fa22584230..f089f9a74da229b115746e15ac60c3e01bc3b7cb 100644 (file)
--- a/src/test/regress/sql/generated.sql
+++ b/src/test/regress/sql/generated.sql
@@ -89,11 +89,31 @@ INSERT INTO gtest1_1 VALUES (4);
 SELECT * FROM gtest1_1;
 SELECT * FROM gtest1;
 
--- test inheritance mismatch
+CREATE TABLE gtest_normal (a int, b int);
+CREATE TABLE gtest_normal_child (a int, b int GENERATED ALWAYS AS (a * 2) STORED) INHERITS (gtest_normal);
+\d gtest_normal_child
+INSERT INTO gtest_normal (a) VALUES (1);
+INSERT INTO gtest_normal_child (a) VALUES (2);
+SELECT * FROM gtest_normal;
+
+-- test inheritance mismatches between parent and child
+CREATE TABLE gtestx (x int, b int GENERATED ALWAYS AS (a * 22) STORED) INHERITS (gtest1);  -- error
+CREATE TABLE gtestx (x int, b int DEFAULT 10) INHERITS (gtest1);  -- error
+CREATE TABLE gtestx (x int, b int GENERATED ALWAYS AS IDENTITY) INHERITS (gtest1);  -- error
+
+-- test multiple inheritance mismatches
 CREATE TABLE gtesty (x int, b int);
 CREATE TABLE gtest1_2 () INHERITS (gtest1, gtesty);  -- error
 DROP TABLE gtesty;
 
+CREATE TABLE gtesty (x int, b int GENERATED ALWAYS AS (x * 22) STORED);
+CREATE TABLE gtest1_2 () INHERITS (gtest1, gtesty);  -- error
+DROP TABLE gtesty;
+
+CREATE TABLE gtesty (x int, b int DEFAULT 55);
+CREATE TABLE gtest1_2 () INHERITS (gtest0, gtesty);  -- error
+DROP TABLE gtesty;
+
 -- test stored update
 CREATE TABLE gtest3 (a int, b int GENERATED ALWAYS AS (a * 3) STORED);
 INSERT INTO gtest3 (a) VALUES (1), (2), (3), (NULL);