Pavel Stehule <pavel.steh...@gmail.com> writes:
> I am solving a strange situation, where using a view is slower than
> using same tables directly.
> The view is defined as
> CREATE VIEW v1 AS
> SELECT *
> FROM A
> LEFT JOIN B
> LEFT JOIN C
> LEFT JOIN D
> and query is
> SELECT *
> FROM T
> LEFT JOIN v
> this query is slower than:
> SELECT *
> FROM T
> LEFT JOIN A
> LEFT JOIN B
> LEFT JOIN C
> LEFT JOIN D
> Is there a some reason for this behave?
Well, they don't necessarily mean the same thing --- these are only
logically equivalent if the left joins all commute, which would depend
on the ON conditions.
> [ EXPLAIN outputs ]
But I also notice that you are using collapse/geqo limits of 12 for
queries that involve 13 base relations, so that'd mean that syntactic
differences could lead to plan differences too.
regards, tom lane
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