This commit implements the automatic conversion of 'x IN (VALUES ...)' into
ScalarArrayOpExpr. That simplifies the query tree, eliminating the appearance
of an unnecessary join.
Since VALUES describes a relational table, and the value of such a list is
a table row, the optimizer will likely face an underestimation problem due to
the inability to estimate cardinality through MCV statistics. The cardinality
evaluation mechanism can work with the array inclusion check operation.
If the array is small enough (< 100 elements), it will perform a statistical
evaluation element by element.
We perform the transformation in the convert_ANY_sublink_to_join() if VALUES
RTE is proper and the transformation is convertible. The conversion is only
possible for operations on scalar values, not rows. Also, we currently
support the transformation only when it ends up with a constant array.
Otherwise, the evaluation of non-hashed SAOP might be slower than the
corresponding Hash Join with VALUES.
Discussion: https://postgr.es/m/0184212d-1248-4f1f-a42d-f5cb1c1976d2%40tantorlabs.com
Author: Alena Rybakina <a.rybakina@postgrespro.ru>
Author: Andrei Lepikhov <lepihov@gmail.com>
Reviewed-by: Ivan Kush <ivan.kush@tantorlabs.com>
Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com>
c0962a113d