Re: SQL 'in' vs join.

Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
>> Now that the executor understands about multiple join rules (for
>> OUTER JOIN support), I've been thinking about inventing a new join rule
>> that says "at most one output row per left-hand row" --- this'd be sort
>> of the opposite of the LEFT OUTER JOIN rule, "at least one output row
>> per left-hand row" --- and then transforming IN (sub-select) clauses
>> that appear at the top level of WHERE into this kind of join. Won't
>> happen for 7.1, though.

> Of course, we will have the query tree redesign for 7.2, right, make
> that unnecessary.

No, I see that as part of the query tree redesign. You'd still need
executor support as above, but what remains to be seen is how hard is it
for the planner to do the transformation I so blithely posited ... and
do we need to change the querytree structure to make it easier?

regards, tom lane