[GitHub] [arrow-datafusion] Dandandan commented on pull request #288: [Datafusion] NOW() function support

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Dandandan commented on pull request #288:
URL: https://github.com/apache/arrow-datafusion/pull/288#issuecomment-835811345


   @msathis
   
   Thanks for this PR!
   
   I believe we should do it a bit differently and not calculate the timestamp inside the optimization rule.
   
   One could disable the optimization rule, or execute an un-optimized plan.
   The result of the query needs to be correct in those cases too.
   
   My suggestion would be to set field to the `ExecutionContextState` (something like `queryExecutionStartTime`) at the start of a query and pass it to the optimizers / evaluation code. This requires maybe some more changes to the code, but is needed to correctly run the queries.
   
   For the optimizer you could use `utils::expr_sub_expressions` (see use in filter push down) to recurse into the expressions and replace *all* cases of the `NOW` with the timestamp of the start of the query.
   
   


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