Alexey Klyukin <alexk(at)hintbits(dot)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