[GitHub] [arrow-datafusion] ygf11 commented on issue #4140: Support more expressions in equality join

[GitBox <gi...@apache.org>]

ygf11 commented on issue #4140:
URL: https://github.com/apache/arrow-datafusion/issues/4140#issuecomment-1308103957

   > maybe it related to the subquery and the type coercion.
   
   Yes, it is relative to `type coercion`.
   
   The issue is not very detailed, Let me add a little more.
   Currently our `LogicalPlan::Join(..)` only supports `column equality` for join, so does physical plan.
   
   https://github.com/apache/arrow-datafusion/blob/a32fb657d1caec634cb53979b2f7ef2fad224905/datafusion/expr/src/logical_plan/plan.rs#L1488
   
   https://github.com/apache/arrow-datafusion/blob/a32fb657d1caec634cb53979b2f7ef2fad224905/datafusion/core/src/physical_plan/joins/hash_join.rs#L125
   
   We can extend `column` to `normal expression`, then datafusion can support more equality joins.
   
   That means:
   * If all columns of left side expression are in the left schema, and so does right side, parse as `equality joins`. 
   * Other wise, parse as `cross join`.
   
   For #2877, since the join unit is expression, we can wrap `cast` in `type coercion` phase when data types of two side is not same.
   
   
   
   
   
   
   


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