Re: BUG #16176: NULL value returned by category_sql argument to crosstab() causes segmentation fault

PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
> -- this will crash pg12, but not version() < 12 - note NULL value in
> categories query:
> select * from crosstab ('values (1, 2, 12), (1, 3, 13), (2, 2, 22), (2,
> 3, 23), (3, 2, 32), (3, 3, 33) order by 1, 2, 3', 'values (2), (null)') as
> rr (a int, "2" int, "3" int);

Yeah, duplicated here. It seems tablefunc is passing a NULL string
pointer to sprintf(). Previously, that would work on some platforms
and crash on others --- as of v12, it crashes everywhere.

What we need here is to figure out what the hashtab string key ought
to be for a NULL category. I suspect what was happening before
(on non-crashing platforms) was that you implicitly got "(nil)"
or some spelling like that, which is not great because it could
conflict with a valid user key. Alternatively, we could refuse
NULL category values ... not sure if that's desirable.

Anyway, this is *not* a new bug, it's just possible to hit it on
more platforms now.

regards, tom lane