[GitHub] [arrow-datafusion] Jimexist commented on issue #554: implement lead and lag with 2nd and 3rd argument

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

Jimexist commented on issue #554:
URL: https://github.com/apache/arrow-datafusion/issues/554#issuecomment-873545732


   > Hi @Jimexist, Could I take a look at this ?
   > 
   > 
   > 
   > As I understand it:
   > 
   > * a **BuiltInWindowFunctionExpr** and a **PartitionEvaluator** has to be implemented under _physical_plan/expressions_, **lag** and **lead** functions should be created with a name, an expression, and the offset/default_value optional arguments.
   > 
   > 
   > 
   > * **return_type_for_built_in** and **signature_for_built_in** should be changed for Lag/Lead (physical_plan/window_functions)
   > 
   > 
   > 
   > * signature has to be a **Signature::OneOf**( (expr -> result), (expr, offset) -> result, (expr, offset, default_value) -> result )
   > 
   > 
   > 
   > I'm probably missing some details, but would this approach be valid ?
   
   Go ahead and thanks!
   
   the way is see it currently there is no easy way to express heterogeneity in arg types so i would stick with any and check inside the actual execution phase. 


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