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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