Github user dilipbiswal commented on a diff in the pull request:

    https://github.com/apache/spark/pull/22326#discussion_r214840118
  
    --- Diff: 
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
 ---
    @@ -1208,9 +1208,26 @@ object PushPredicateThroughJoin extends 
Rule[LogicalPlan] with PredicateHelper {
                 reduceLeftOption(And).map(Filter(_, left)).getOrElse(left)
               val newRight = rightJoinConditions.
                 reduceLeftOption(And).map(Filter(_, right)).getOrElse(right)
    -          val newJoinCond = commonJoinCondition.reduceLeftOption(And)
    -
    -          Join(newLeft, newRight, joinType, newJoinCond)
    +          val (newJoinConditions, others) =
    +            commonJoinCondition.partition(canEvaluateWithinJoin)
    +          val newJoinCond = newJoinConditions.reduceLeftOption(And)
    +          // if condition expression is unevaluable, it will be removed 
from
    +          // the new join conditions, if all conditions is unevaluable, we 
should
    +          // change the join type to CrossJoin.
    +          val newJoinType =
    +            if (commonJoinCondition.nonEmpty && newJoinCond.isEmpty) {
    +              logWarning(s"The whole 
commonJoinCondition:$commonJoinCondition of the join " +
    +                s"plan:\n $j is unevaluable, it will be ignored and the 
join plan will be " +
    --- End diff --
    
    @mgaido91 Thanks. Marco, do you know if there are instances when we pick 
cross join implicitly ? It wouldn't perform very well, right ? Wondering if we 
should error out or pick a bad plan. I guess, i am not sure whats the right 
thing to do here. 


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