Re: BUG #18594: CASE WHEN ELSE failing to return the expected output when the same colum is used in WHEN and ELSE - Mailing list pgsql-bugs

Francisco J. Ossandón <fco.j.ossandon@gmail.com> writes:
> So is the ELSE column hijacking the data type of the whole expression?

It's the only CASE result that is supplying a definite type at all.
But see

https://www.postgresql.org/docs/current/typeconv-union-case.html

particularly the footnote to the bit about "Select the first
non-unknown input type as the candidate type, then consider
each other non-unknown input type, left to right."

The WHEN clauses have exactly nothing to do with the result type
of the CASE: it's the THEN and ELSE clauses that supply the result.

                        regards, tom lane