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Disallow USING clause when altering type of generated column

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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 478846e768
commit 4d68a04324
2 changed files with 14 additions and 2 deletions
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13
src/backend/commands/tablecmds.c
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@ -12677,6 +12677,16 @@ 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
@ -12753,11 +12763,12 @@ 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 */