"Julian Scarfe" <julian@xxxxxxxxxxx> writes:
> From: "Tom Lane" <tgl@xxxxxxxxxxxxx>
>> The
>> problem you've got is that you need a nestloop-with-inner-indexscan
>> plan type, where the inner side is an Append group (that is, an
>> inheritance tree) --- and 8.1 doesn't know how to create such a plan.
>> If you can update to 8.2 or later it should get better.
> Isn't test 3 (scalar subqueries) also a nestloop-with-inner-indexscan with
> an inner Append?
No. The subquery is planned separately and sees the upper query's
variable as a pseudo-constant Param. In neither query does the
planner think that a join is happening.
regards, tom lane
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