Hi Ilia,
I checked v4. A few more cases could be simplified:
create table t(a int);
insert into t values (1), (42), (null);
explain (costs off)
select * from t where (a not in (42, null)) is true;
explain (costs off)
select * from t where (a not in (42, null)) is not true;
Both plans still contain the array comparison. The first condition
could be folded to false, and the second to true.
A null array is another case:
explain (costs off)
select * from t where a <> all (null::int[]);
explain (costs off)
select * from t where a = any (null::int[]);
Both plans still contain the array comparison. These comparisons
always return null, so in a where clause they could be folded
to false.
The comment in saop_never_true() says that ordinary constant folding
handles a null array, but this does not happen when the left argument
is a column.
Could you cover these cases and add regression tests?
Best regards,
Denis Smirnov
