wiedld commented on code in PR #14356:
URL: https://github.com/apache/datafusion/pull/14356#discussion_r1936790068
##########
datafusion/expr/src/logical_plan/plan.rs:
##########
@@ -2645,6 +2643,106 @@ pub struct Union {
pub schema: DFSchemaRef,
}
+impl Union {
+ /// Constructs new Union instance deriving schema from inputs.
+ fn try_new(inputs: Vec<Arc<LogicalPlan>>) -> Result<Self> {
+ let schema = Self::derive_schema_from_inputs(&inputs, false)?;
+ Ok(Union { inputs, schema })
+ }
+
+ /// Constructs new Union instance deriving schema from inputs.
+ /// Inputs do not have to have matching types and produced schema will
+ /// take type from the first input.
+ pub fn try_new_with_loose_types(inputs: Vec<Arc<LogicalPlan>>) ->
Result<Self> {
+ let schema = Self::derive_schema_from_inputs(&inputs, true)?;
+ Ok(Union { inputs, schema })
+ }
+
+ /// Constructs new Union instance deriving schema from inputs.
+ ///
+ /// `loose_types` if true, inputs do not have to have matching types and
produced schema will
+ /// take type from the first input. TODO this is not necessarily
reasonable behavior.
+ fn derive_schema_from_inputs(
+ inputs: &[Arc<LogicalPlan>],
+ loose_types: bool,
+ ) -> Result<DFSchemaRef> {
+ if inputs.len() < 2 {
Review Comment:
Making sure I understand the use case. If I want to construct a UNION
logical plan with different types that are coercible (be it by current builtin
rules or future user-defined rules), then I would use the
`Union::try_new_with_loose_types` and have the analyzer pass handle coercion.
Is this right?
Then what exactly is the use case for the `Union::try_new`? Since it's used
in the schema recompute which can occur after the analyzer type coercion. Do we
therefore need it to always perform proper coercion, including any future
user-defined coercion rules?
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