This patch improves handling of NULLs in textual fields in ColumnStore.
Previously empty strings were considered NULLs and it could be a problem
if data scheme allows for empty strings. It was also one of major
reasons of behavior difference between ColumnStore and other engines in
MariaDB family.
Also, this patch fixes some other bugs and incorrect behavior, for
example, incorrect comparison for "column <= ''" which evaluates to
constant True for all purposes before this patch.
This patch fixes a wrong `join id` assignment for `TupleHashJoinStep` in a view.
After MCOL-334 CS assigns a '-1' as `join id` for `TupleHashJoinStep` in a view, and
in this case we cannot apply a filter for specific `Join step`, which is associated with `join id`
for 2 reasons:
1. Filters for all `TupleHashJoinSteps` associated with the same `join id`, which is '-1'.
2. When CS creates a `joinIdIndexMap` it eliminates all `join ids` which a less or equal 0.
This patch also fixes some tests for the view, which were generated wrong results.
