Pavel, * Pavel Stehule (pavel.steh...@gmail.com) wrote: > I found some crazy queries in one customer application. These queries are > stupid, but it was surprise for me so there are not some simple optimization > > create table foo(a int); > insert into foo select generate_series(1,100000); > analyze foo; > explain select * from foo where a <> a; > > It does full scan of foo, although it should be replaced by false in > planner time.
a <> a could go to NULL. Obviously, that'll be false for such a simple case, but it might not work out that way in a more complicated WHERE clause. > Same issue is a expression a = a .. can be replaced by true a = a can't be replaced unless you know that 'a' can't be NULL. In short, fix the application. Thanks! Stephen
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