From 53977598174652dcb06bc2b26674c29b9ae601cc Mon Sep 17 00:00:00 2001 From: Peter Eisentraut Date: Tue, 3 Nov 2020 15:14:50 +0100 Subject: [PATCH] Disallow ALTER TABLE ONLY / DROP EXPRESSION The current implementation cannot handle this correctly, so just forbid it for now. GENERATED clauses must be attached to the column definition and cannot be added later like DEFAULT, so if a child table has a generation expression that the parent does not have, the child column will necessarily be an attlocal column. So to implement ALTER TABLE ONLY / DROP EXPRESSION, we'd need extra code to update attislocal of the direct child tables, somewhat similar to how DROP COLUMN does it, so that the resulting state can be properly dumped and restored. Discussion: https://www.postgresql.org/message-id/flat/15830.1575468847%40sss.pgh.pa.us --- src/backend/commands/tablecmds.c | 22 +++++++++++++++++++--- src/test/regress/expected/generated.out | 11 ++++++----- src/test/regress/sql/generated.sql | 2 +- 3 files changed, 26 insertions(+), 9 deletions(-) diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c index b7e470ccc9b..0a6ccb28808 100644 --- a/src/backend/commands/tablecmds.c +++ b/src/backend/commands/tablecmds.c @@ -412,7 +412,7 @@ static ObjectAddress ATExecAddIdentity(Relation rel, const char *colName, static ObjectAddress ATExecSetIdentity(Relation rel, const char *colName, Node *def, LOCKMODE lockmode); static ObjectAddress ATExecDropIdentity(Relation rel, const char *colName, bool missing_ok, LOCKMODE lockmode); -static void ATPrepDropExpression(Relation rel, AlterTableCmd *cmd, bool recursing); +static void ATPrepDropExpression(Relation rel, AlterTableCmd *cmd, bool recurse, bool recursing, LOCKMODE lockmode); static ObjectAddress ATExecDropExpression(Relation rel, const char *colName, bool missing_ok, LOCKMODE lockmode); static ObjectAddress ATExecSetStatistics(Relation rel, const char *colName, int16 colNum, Node *newValue, LOCKMODE lockmode); @@ -4141,7 +4141,7 @@ ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd, case AT_DropExpression: /* ALTER COLUMN DROP EXPRESSION */ ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE); ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode, context); - ATPrepDropExpression(rel, cmd, recursing); + ATPrepDropExpression(rel, cmd, recurse, recursing, lockmode); pass = AT_PASS_DROP; break; case AT_SetStatistics: /* ALTER COLUMN SET STATISTICS */ @@ -7238,8 +7238,24 @@ ATExecDropIdentity(Relation rel, const char *colName, bool missing_ok, LOCKMODE * ALTER TABLE ALTER COLUMN DROP EXPRESSION */ static void -ATPrepDropExpression(Relation rel, AlterTableCmd *cmd, bool recursing) +ATPrepDropExpression(Relation rel, AlterTableCmd *cmd, bool recurse, bool recursing, LOCKMODE lockmode) { + /* + * Reject ONLY if there are child tables. We could implement this, but it + * is a bit complicated. GENERATED clauses must be attached to the column + * definition and cannot be added later like DEFAULT, so if a child table + * has a generation expression that the parent does not have, the child + * column will necessarily be an attlocal column. So to implement ONLY + * here, we'd need extra code to update attislocal of the direct child + * tables, somewhat similar to how DROP COLUMN does it, so that the + * resulting state can be properly dumped and restored. + */ + if (!recurse && + find_inheritance_children(RelationGetRelid(rel), lockmode)) + ereport(ERROR, + (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), + errmsg("ALTER TABLE / DROP EXPRESSION must be applied to child tables too"))); + /* * Cannot drop generation expression from inherited columns. */ diff --git a/src/test/regress/expected/generated.out b/src/test/regress/expected/generated.out index 7ccc3c65ed1..4b062603044 100644 --- a/src/test/regress/expected/generated.out +++ b/src/test/regress/expected/generated.out @@ -805,13 +805,14 @@ CREATE TABLE gtest30 ( b int GENERATED ALWAYS AS (a * 2) STORED ); CREATE TABLE gtest30_1 () INHERITS (gtest30); -ALTER TABLE ONLY gtest30 ALTER COLUMN b DROP EXPRESSION; +ALTER TABLE ONLY gtest30 ALTER COLUMN b DROP EXPRESSION; -- error +ERROR: ALTER TABLE / DROP EXPRESSION must be applied to child tables too \d gtest30 - Table "public.gtest30" - Column | Type | Collation | Nullable | Default ---------+---------+-----------+----------+--------- + Table "public.gtest30" + Column | Type | Collation | Nullable | Default +--------+---------+-----------+----------+------------------------------------ a | integer | | | - b | integer | | | + b | integer | | | generated always as (a * 2) stored Number of child tables: 1 (Use \d+ to list them.) \d gtest30_1 diff --git a/src/test/regress/sql/generated.sql b/src/test/regress/sql/generated.sql index 4cff1279c77..c86ad34b006 100644 --- a/src/test/regress/sql/generated.sql +++ b/src/test/regress/sql/generated.sql @@ -411,7 +411,7 @@ CREATE TABLE gtest30 ( b int GENERATED ALWAYS AS (a * 2) STORED ); CREATE TABLE gtest30_1 () INHERITS (gtest30); -ALTER TABLE ONLY gtest30 ALTER COLUMN b DROP EXPRESSION; +ALTER TABLE ONLY gtest30 ALTER COLUMN b DROP EXPRESSION; -- error \d gtest30 \d gtest30_1 ALTER TABLE gtest30_1 ALTER COLUMN b DROP EXPRESSION; -- error