[GitHub] [spark] peter-toth commented on issue #27518: [WIP][SPARK-30768][SQL] Constraints should be inferred from inequality attributes

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peter-toth commented on issue #27518: [WIP][SPARK-30768][SQL] Constraints should be inferred from inequality attributes
URL: https://github.com/apache/spark/pull/27518#issuecomment-585251432
 
 
   @wangyum, I'm a but confused now. As far as I see based on your changes, in this PR you substitute `attribute = constant` form of constraints into other constraints to infer new constraints.
   So this PR will help with your example query as from `select t1.* from SPARK_30768_1 t1 join SPARK_30768_2 t2 on (t1.c1 > t2.c1) where t1.c1 = 3` the new constraint `3 > t2.c1` is inferred.
   It will also help with those cases I mentioned:
   `select t1.* from SPARK_30768_1 t1 join SPARK_30768_2 t2 on abs(t1.c1) = t2.c1 where t1.c1 = 3` as `abs(3) = t2.c1` will be inferred.
   It will also help here: https://github.com/apache/spark/pull/27252#discussion_r378184866 as after both this PR **and** https://github.com/apache/spark/pull/27252 are merged. It will solve the issue in the comment of @cloud-fan:
   > If we have cast(a, dt) = b and a = 1, seems we can also infer cast(1, dt) = b
   
   But, I don't see how it will help with the example query here: https://github.com/apache/spark/pull/27518#issuecomment-585189218
   

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