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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.

Reported-by: Jian He <jian.universality@gmail.com>
Reviewed-by: Yugo NAGATA <nagata@sraoss.co.jp>
Discussion: https://www.postgresql.org/message-id/flat/c7083982-69f4-4b14-8315-f9ddb20b9834%40eisentraut.org
This commit is contained in:
Peter Eisentraut 2024-08-29 08:38:29 +02:00
parent 5d9170697e
commit cf49a606c4
2 changed files with 14 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
src/backend/commands/tablecmds.c
View File

@ -12307,6 +12307,16 @@ 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_COLUMN_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
@ -12383,11 +12393,12 @@ ATPrepAlterColumnType(List **wqueue,
(errcode(ERRCODE_DATATYPE_MISMATCH),
errmsg("column \"%s\" cannot be cast automatically to type %s",
colName, format_type_be(targettype)),
!attTup->attgenerated ?
/* translator: USING is SQL, don't translate it */
errhint("You might need to specify \"USING %s::%s\".",
quote_identifier(colName),
format_type_with_typemod(targettype,
targettypmod))));
targettypmod)) : 0));
}
/* Fix collations after all else */

3
src/test/regress/expected/generated.out
View File

@ -836,7 +836,8 @@ 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.