jonahgao opened a new pull request, #11961:
URL: https://github.com/apache/datafusion/pull/11961
## Which issue does this PR close?
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Closes #11742.
## Rationale for this change
Currently, in the LogicalPlan builder, we coerce the inputs of a union plan
to a common schema.
But this common schema is inaccurate because it lacks type coercion for
expressions.
For example, in #11742, the return type of the expression `nvl(v1, 0.5)` is
INT before type coercion and will become Float64 afterward.
```rust
/// The return type of `nvl` depends on the type of the first argument.
fn return_type(&self, arg_types: &[DataType]) -> Result<DataType> {
Ok(arg_types[0].clone())
}
```
The fix is to place coercion of the union after the type coercion of
expressions.
## What changes are included in this PR?
- Move coercion of union from builder to `TypeCoercion`.
- Move some union-related SQL planner tests to slt, as these tests need to
perform type coercion to achieve the same results as before.
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## Are these changes tested?
Yes
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## Are there any user-facing changes?
Yes
`project_with_column_index` has become private. It was introduced for UNION
in #2108, and I think it should only be used internally.
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