On 9 February 2016 at 14:53, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> SELECT COALESCE((SELECT 'Yes' FROM gwtest WHERE id=4), 'No') AS valid;
>
> There's no null visible anywhere in that. I suppose that if there's
> no row with id=4, there would be a null at runtime,
Well yes, that was the whole point.
> but that's not
> going to make any difference for parse-time determination of what
> type the COALESCE() will return.
But when the gwtest subquery _does_ return a value it works, so the
problem can't be parse-time determination, can it?
Geoff
