Kim Johan Andersson <kimjand@xxxxxxxxx> writes: > [ uses partial index: ] > EXPLAIN (analyze, costs, buffers, verbose) SELECT val FROM > table_test_enum WHERE val = 'Ole' and dat IS NULL; > > [ doesn't: ] > PREPARE qry1(varchar) AS SELECT val FROM table_test_enum WHERE val = > $1::type_table_test_enum AND dat IS NULL; There's no actual cast from varchar to that enum type. The system is letting you get away with it anyway, by applying what's called a CoerceViaIO cast --- which means convert the varchar to a simple string (cstring) and then apply enum_in(). Unfortunately for you, enum_in() is marked stable not immutable (probably on the grounds that it depends on catalog contents) so the expression isn't reduced to a plain constant during constant-folding and thus fails to match the partial index's WHERE clause. In the first case, 'Ole' is taken as a constant of type type_table_test_enum right off the bat, as was the same constant in the index's WHERE clause, so everything matches fine. (This seems a little inconsistent now that I think about it --- if it's okay to fold the literal to an enum constant at parse time, why can't we do the equivalent at plan time? But these rules have stood for a good while so I'm hesitant to change them.) Anyway, the recommendable solution is the one you already found: declare the PREPARE's argument as type_table_test_enum not varchar. regards, tom lane
