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[SPARK-20121][SQL] simplify NullPropagation with NullIntolerant #17450
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Is the function SUBSTRING null-intolerant? What is the return value if
str
is a null value?There was a problem hiding this comment.
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Ref: https://www.ibm.com/support/knowledgecenter/en/SSEPEK_10.0.0/sqlref/src/tpc/db2z_bif_substr.html
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I might be confused with the terminologies: NullIntolerant expression versus "null-intolerant predicate". But if SUBSTRING is marked null-intolerant expression, why do we not mark the class of string functions such as STARTSWITH, etc. the same way? Am I missing anything here?
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Yes, we should mark
NullIntolerant
to the other expressions, if possible, and also update the document.There was a problem hiding this comment.
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@nsyca If you have a bandwidth, could you please review all the expressions and see whether they can be marked as
NullIntolerant
?You can check the impl of these expressions and compare them with the corresponding ones in the other RDBMS. Thanks!
Below is a ref PR you can use: https://github.com/apache/spark/pull/15850/files. You can continue my work if you want.
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I will certainly take a look. On a second thought, since "most" of the SQL functions are null-intolerant, isn't easier to mark only functions that are null-tolerant such as ISNOTNULL? I am just pitching an idea here, not indicating we should abandon this PR.
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At the beginning, when we introduce
NullIntolerant
, @marmbrus said we should do it more carefully. We prefer to using the white-list solution for avoiding hidden bugs. Marking itNullIntolerant
if and only if we are ensure that they are null intolerant. Thus, when we doing it, we should also add the corresponding test cases and documents.