findepi opened a new pull request, #14349:
URL: https://github.com/apache/datafusion/pull/14349
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.
- Fixes https://github.com/apache/datafusion/issues/14343
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