Backport: Fix incorrect searched CASE optimization, Fix UNION field nullability tracking #78
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This cherry pick a snapshot of a PR offered upstream.
------------------------------------------------------
There is an optimization for searched CASE where values are of boolean
type. It was converting the expression like
CASE
WHEN X THEN A
WHEN Y THEN B
..
[ ELSE D ]
END
into
(X AND A)
OR (Y AND NOT X AND B)
[ OR (NOT (X OR Y) AND D) ]
This had the following problems
- does not work for nullable conditions. If X is nullable, we cannot use
NOT (X) to compliment it. We need to use `X IS DISTINCT FROM true`
- it does not work correctly when some conditions are nullable and other
values are false. E.g. X=NULL, A=true, Y=NULL, B=true, D=false, the
CASE should return false, but the boolean expression will simplify to
`(NULL AND ..) OR (NULL AND ..) OR (false)` which is NULL, not false
- thus we use `X` for truthness check of `X`, we need to test `X IS
NOT DISTINCT FROM true`
- it did not work correctly when default D is missing, but conditions
do not evaluate to NULL. CASE's result should be NULL but was false.
This commit fixes that optimization.
This cherry pick a snapshot of a PR offered upstream. ------------------------------------------------------ This commit fixes two bugs related to UNION handling - when constructing union plan nullability of the other union branch was ignored, thus resulting field could easily have incorrect nullability - when pruning/simplifying projects, in `recompute_schema` function there was similar logic, thus loosing nullability information even for correctly constructed Union plan node As a result, other optimizer logic (e.g. `expr_simplifier.rs`) could draw incorrect conclusions and thus lead to incorrect query results, as demonstrated with the attached SLT test.
sadboy
approved these changes
Jan 30, 2025
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This is
backportsnapshot of PRs:Let's cherry pick those solutions to the fork to unblock further work.