Re: Lack of index usage when doing array casts

Alexey Klyukin <alexk@hintbits.com> writes:
> We had a problem with PostgreSQL not using an index scan in 2 similar
> queries, the only difference between them is the array cast from text[] to
> location_type[] (array of enum values).

Hmm.  IIRC the text to enum cast is considered stable not immutable, which
is why that doesn't get folded to a Const on sight.  However, it seems
like it'd be okay for scalararraysel() to reduce stable expressions for
estimation purposes, ie it should be using estimate_expression_value.

            regards, tom lane