Takahiro Itagaki <itagaki.takahiro@oss.ntt.co.jp> writes:
> * In the regression tests, almost all of them don't have ORDER BY clause.
> They just work, but we might need ORDER BY to get robust output.
> What did we do in other regression tests?
We add ORDER BY only when experience shows it's necessary. The
reasoning is explained in regress.sgml:
You might wonder why we don't order all the regression test queries explicitly
to get rid of this issue once and for all. The reason is that that would
make the regression tests less useful, not more, since they'd tend
to exercise query plan types that produce ordered results to the
exclusion of those that don't.
regards, tom lane