[GitHub] [arrow-datafusion] alamb commented on a diff in pull request #6654: fix: 'datatrunc' return inconsistent type

["alamb (via GitHub)" <gi...@apache.org>]

alamb commented on code in PR #6654:
URL: https://github.com/apache/arrow-datafusion/pull/6654#discussion_r1227334439


##########
datafusion/physical-expr/src/datetime_expressions.rs:
##########
@@ -294,16 +294,24 @@ pub fn date_trunc(args: &[ColumnarValue]) -> Result<ColumnarValue> {
                 }
                 "second" => {
                     // trunc to second
-                    let mill = ScalarValue::TimestampNanosecond(

Review Comment:
   I think we would have to change the values returned by https://github.com/apache/arrow-datafusion/pull/6654/files#diff-67ae8808785b2e651767d7ff67dd7c53be04ca098857b52c82ed19927e071cdaL322 as well as the type returned by `BuiltInScalarFunction::return_type`
   
   otherwise we'll be in the situation again where the scalar implementation does something different than the array implementation
   
   However, I was surprised that there were no tests that failed which reveals a gap in our test coverage. I wrote the test in https://github.com/apache/arrow-datafusion/pull/6655 which does pass on `main` but fails on this PR



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