Hi: I wrote a patch to erase the distinctClause if the result is unique by definition, I find this because a user switch this code from oracle to PG and find the performance is bad due to this, so I adapt pg for this as well.
This patch doesn't work for a well-written SQL, but some drawback of a SQL may be not very obvious, since the cost of checking is pretty low as well, so I think it would be ok to add.. Please see the patch for details. Thank you.
0001-Erase-the-distinctClause-if-the-result-is-unique-by-.patch
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