#699 fix return type conflict when calling builtin math fuctions

[lvheyang]

Which issue does this PR close?

Closes #699

Rationale for this change

When we infer schema we should also consider the input arguments' datatype. such as sqrt(f32) -> f32, sqrt(64) -> f64. But now builtin functions statically return Float64. It causes column types and schema types conflict.

What changes are included in this PR?

Change the return type in datafusion/src/physical_plan/functions.rs. This PR made builtin math functions return the same type as the input argument

Are there any user-facing changes?

[alamb]

Thank you @lvheyang -- I think this is on the right track. I will comment more on #699 as well

[alamb]

This is looking good to me -- thank you @lvheyang !

I think all this PR needs to be mergeable are some tests (either in context.rs or sql.rs) of running math queries against columns that have float32, int etc.

Let me know if you would like some help or more specific pointers

[lvheyang]

Thanks for your kind help! @alamb I added test cases in context.rs, test SQLs:

1. SELECT sqrt(f64) FROM t
2. SELECT sqrt(f32) FROM t // would panic before this pull request
3. SELECT sqrt(i64) FROM t
4. SELECT sqrt(i32) FROM t

Is there any case else needed?

[houqp]

@lvheyang see https://github.com/apache/arrow-rs/blob/f1a831f/arrow/src/array/array.rs#L234-L244 for numeric types with other bit width.

[lvheyang]

@houqp 👌, I will add them all in the test case.

[lvheyang]

@alamb @houqp test case added. The case covered int8/int16/int32/int64/uint8/uint16/uint32/uint64/float32/float64. Please review. Thanks a lot!

[alamb]

This looks like an improvement to me. Thank you @lvheyang !

[alamb]

👍 it is a good test. We can finagle the types later if needed (e.g. if we ever want to support sqrt(numeric) --> numeric.

I think this PR makes DataFusion better than it is on master.

[alamb]

Any thoughts @Dandandan or @jorgecarleitao ?

[alamb]

Thank you again for the contribution @lvheyang .