Re: BUG #17465: Wrong error message while trying to change system column type.

PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
> accidentally I tried to change a system column data type on Windows and got
> a strange error message "no owned sequence found":

> postgres=# alter table t1 alter column cmin type text;
> ERROR: no owned sequence found
> postgres=# alter table t1 alter column cmax type text;
> ERROR: cannot alter system column "cmax"

Yeah, same here.

> I think the ATParseTransformCmd() function needs the same check as the check
> in the ATPrepAlterColumnType() function.

That seems pretty duplicative. I think it's sufficient to do something
like

- if (TupleDescAttr(tupdesc, attnum - 1)->attidentity)
+ if (attnum > 0 &&
+ TupleDescAttr(tupdesc, attnum - 1)->attidentity)

in the faulty code, and let the actual error message come out where
it does now.

Will fix, thanks for the report!

regards, tom lane