Github user chenghao-intel commented on the pull request:
https://github.com/apache/spark/pull/482#issuecomment-41235600
I have 2 options for the changes:
Option 1) is add an new method in expression, which tells the optimize
rule, what it produces if part of its arguments are "always be null" /
"possibly be null" / "never be null". the rule may test every expressions.
Option 2) the rule itself enumerates all of the expressions, and understand
what if part of the arguments is "always be null" etc., like the
BooleanSimplification does.
But still seems the "constraint propagation" is the best. Not sure if you
have better idea on this.
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