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From arina-ielchiieva <...@git.apache.org>
Subject [GitHub] drill issue #794: DRILL-5375: Nested loop join: return correct result for le...
Date Wed, 29 Mar 2017 10:41:12 GMT
Github user arina-ielchiieva commented on the issue:

    https://github.com/apache/drill/pull/794
  
    
    Thanks for bringing up this point. I have done some investigation and found out that implicit
casts for nested loop join are already included during materialization.
    Join condition is transformed into FunctionCall [1] which is later on materialized using
ExpressionTreeMaterializer [2]. 
    `ExpressionTreeMaterializer.visitFunctionCall` includes section which implicit casts [3].
    Actually these casts are more enhanced that during hash and merge joins.
    For example, during hash and merge joins only casts between numeric types, date and timestamp,
varchar and varbinary are supported, i.e.
    join by int and varchar columns won't be performed. The following error will be returned:
`Join only supports implicit casts between 1. Numeric data
     2. Varchar, Varbinary data 3. Date, Timestamp data Left type: INT, Right type: VARCHAR.
Add explicit casts to avoid this error`. 
    In our case nested loop join will be able to perform join by int and varchar columns without
adding explicit casts.
    
    [1] https://github.com/arina-ielchiieva/drill/blob/71628e70a525d9bd27b4f5f56259dce84c75154d/exec/java-exec/src/main/java/org/apache/drill/exec/planner/physical/NestedLoopJoinPrel.java#L95
    [2] https://github.com/arina-ielchiieva/drill/blob/71628e70a525d9bd27b4f5f56259dce84c75154d/exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/join/NestedLoopJoinBatch.java#L265
    [3] https://github.com/apache/drill/blob/9411b26ece34ed8b2f498deea5e41f1901eb1013/exec/java-exec/src/main/java/org/apache/drill/exec/expr/ExpressionTreeMaterializer.java#L362


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