andygrove commented on code in PR #4234:
URL: https://github.com/apache/arrow-datafusion/pull/4234#discussion_r1025837127
##########
datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs:
##########
@@ -760,6 +766,29 @@ impl<'a, S: SimplifyInfo> ExprRewriter for Simplifier<'a,
S> {
},
},
+ // unfold the expression round(source, n)
+ Expr::ScalarFunction {
+ fun: BuiltinScalarFunction::Round,
+ args,
Review Comment:
> Why is that? Could you please give an example?
Sure. Taking Dask SQL as an example, we would want to translate `round(a,
b)` to a call to a Python function to perform the rounding (perhaps in numpy).
With this PR, the logical plan now has a complex expression that is specific to
the DataFusion implementation. Dask SQL would have to undo the `pow` logic here
to get back to the original parameters to `round` so that it can pass them to
numpy.
```
Projection: round(CAST(test.column_1 AS Float64) * Float64(0.01)) /
Float64(0.01) AS round(test.column_1,Int64(-2))
```
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