liukun4515 opened a new issue #1356: URL: https://github.com/apache/arrow-datafusion/issues/1356
**Describe the bug** In the [Implement DECIMAL type](https://github.com/apache/arrow-datafusion/issues/122), I want to implement the decimal data type in datafusion. In the survey period, I take a look the type coercion in the current datafusion, and find some confused points. In this issue, I want to discuss them. For example: - `AggFunction` ``` logical expr： agg(input_exprs) ``` In the expression evaluation, we need to coercion the expr and calc the result type of `ScalarFunction` expr. In the current code, the logical result type use this API[return_type](https://github.com/apache/arrow-datafusion/blob/645a7f484435d7182d88a541ac8cdf8b079b7714/datafusion/src/physical_plan/aggregates.rs#L97), but get the physical expr result type use this API[create_agg_expr](https://github.com/apache/arrow-datafusion/blob/645a7f484435d7182d88a541ac8cdf8b079b7714/datafusion/src/physical_plan/aggregates.rs#L121). These two API have a gap, which is `coerce`. In the `coerce`, the input expr may be added `try_cast` and change the data type, so the inferred result data type may be diff with the logical result data type. **To Reproduce** Steps to reproduce the behavior: **Expected behavior** A clear and concise description of what you expected to happen. **Additional context** Add any other context about the problem here. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
