Bruce Momjian wrote:
>
> We are only going to have subselects in the WHERE clause, not in the
> target list, right?
>
> The standard says we can have them either place, but I didn't think we
> were implementing the target list subselects.
>
> Is that correct?
Yes, this is right for 6.3. I hope that we'll support subselects in
target list, FROM, etc in future.
BTW, I'm going to implement subselect in (let's say) "natural" way -
without substitution of parent query relations into subselect and so on,
but by execution of (correlated) subqueries for each upper query row
(may be with cacheing of results in hash table for better performance).
Sure, this is much more clean way and much more clear how to do this.
This seems like SQL-func way, but funcs start/run/stop Executor each time
when called and this breaks performance.
Vadim