Hello everyone!
I've noticed that COALESCE function doesn't converge to argument
expression if it is alone in argument list of COALESCE as part
simplification routine for expressions in planner. This might suppress
further useful transformations when non-strict ops are required from
some expression like converging OUTER JOIN to INNER one with WHERE qual
containing COALESCE over single column from inner side.
The patch of transformation in question for COALESCE is attached.
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Best regard,
Maksim Milyutin