[SPARK-41668][SQL] DECODE function returns wrong results when passed NULL #39163
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srielau
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…NULL ### What changes were proposed in this pull request? The DECODE function was implemented for Oracle compatibility. It works similar to CASE expression, but it is supposed to have one major difference: NULL == NULL https://docs.oracle.com/database/121/SQLRF/functions057.htm#SQLRF00631 The Spark implementation does not observe this, however: ``` > select decode(null, 6, 'Spark', NULL, 'SQL', 4, 'rocks'); NULL ``` The result is supposed to be 'SQL'. This PR is to fix the issue. ### Why are the changes needed? Bug fix and Oracle compatibility. ### Does this PR introduce _any_ user-facing change? Yes, DECODE function will return matched value when passed null, instead of always returning null. ### How was this patch tested? New UT. Closes #39163 from gengliangwang/fixDecode. Authored-by: Gengliang Wang <gengliang@apache.org> Signed-off-by: Gengliang Wang <gengliang@apache.org> (cherry picked from commit e09fceb) Signed-off-by: Gengliang Wang <gengliang@apache.org>
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What changes were proposed in this pull request?
The DECODE function was implemented for Oracle compatibility. It works similar to CASE expression, but it is supposed to have one major difference: NULL == NULL
https://docs.oracle.com/database/121/SQLRF/functions057.htm#SQLRF00631
The Spark implementation does not observe this, however:
The result is supposed to be 'SQL'. This PR is to fix the issue.
Why are the changes needed?
Bug fix and Oracle compatibility.
Does this PR introduce any user-facing change?
Yes, DECODE function will return matched value when passed null, instead of always returning null.
How was this patch tested?
New UT.