On 21.08.24 09:14, Yugo Nagata wrote:
On Wed, 21 Aug 2024 08:17:45 +0200
Peter Eisentraut <pe...@eisentraut.org> wrote:
A USING clause when altering the type of a generated column does not
make sense. It would write the output of the USING clause into the
converted column, which would violate the generation expression.
This patch adds a check to error out if this is specified.
I’m afraid you forgot to attach the patch.
It seems for me that this fix is reasonable though.
Thanks, here is the patch.
From de331c245f2c1becb2d1c7c7bb34429a18fa85b6 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <pe...@eisentraut.org>
Date: Wed, 21 Aug 2024 08:03:08 +0200
Subject: [PATCH] Disallow USING clause when altering type of generated column
This does not make sense. It would write the output of the USING
clause into the converted column, which would violate the generation
expression. This adds a check to error out if this is specified.
There was a test for this, but that test errored out for a different
reason, so it was not effective.
---
src/backend/commands/tablecmds.c | 10 ++++++++++
src/test/regress/expected/generated.out | 3 ++-
2 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 7a36db6af6d..ee089e393fc 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -12736,6 +12736,16 @@ ATPrepAlterColumnType(List **wqueue,
errmsg("cannot alter system column \"%s\"",
colName)));
+ /*
+ * Cannot specify USING when altering type of a generated column,
because
+ * that would violate the generation expression.
+ */
+ if (attTup->attgenerated && def->cooked_default)
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+ errmsg("cannot specify USING when altering
type of generated column"),
+ errdetail("Column \"%s\" is a generated
column.", colName)));
+
/*
* Don't alter inherited columns. At outer level, there had better not
be
* any inherited definition; when recursing, we assume this was checked
at
diff --git a/src/test/regress/expected/generated.out
b/src/test/regress/expected/generated.out
index 44058db7c1d..499072e14ca 100644
--- a/src/test/regress/expected/generated.out
+++ b/src/test/regress/expected/generated.out
@@ -1026,7 +1026,8 @@ SELECT * FROM gtest27;
(2 rows)
ALTER TABLE gtest27 ALTER COLUMN x TYPE boolean USING x <> 0; -- error
-ERROR: generation expression for column "x" cannot be cast automatically to
type boolean
+ERROR: cannot specify USING when altering type of generated column
+DETAIL: Column "x" is a generated column.
ALTER TABLE gtest27 ALTER COLUMN x DROP DEFAULT; -- error
ERROR: column "x" of relation "gtest27" is a generated column
HINT: Use ALTER TABLE ... ALTER COLUMN ... DROP EXPRESSION instead.
--
2.46.0
