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fix: case expressions type coercion #5796

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fix: case expressions type coercion #5796

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50 changes: 47 additions & 3 deletions datafusion/expr/src/expr_schema.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ use crate::expr::{
};
use crate::field_util::get_indexed_field;
use crate::type_coercion::binary::binary_operator_data_type;
use crate::type_coercion::other::get_coerce_type_for_case_when;
use crate::{aggregate_function, function, window_function};
use arrow::compute::can_cast_types;
use arrow::datatypes::DataType;
Expand Down Expand Up @@ -68,7 +69,25 @@ impl ExprSchemable for Expr {
Expr::OuterReferenceColumn(ty, _) => Ok(ty.clone()),
Expr::ScalarVariable(ty, _) => Ok(ty.clone()),
Expr::Literal(l) => Ok(l.get_datatype()),
Expr::Case(case) => case.when_then_expr[0].1.get_type(schema),
Expr::Case(case) => {
let then_types = case
.when_then_expr
.iter()
.map(|when_then| when_then.1.get_type(schema))
.collect::<Result<Vec<_>>>()?;
let else_type = case
.else_expr
.as_ref()
.map_or(Ok(None), |e| e.get_type(schema).map(Some))?;

get_coerce_type_for_case_when(&then_types, else_type.as_ref()).ok_or_else(
|| {
DataFusionError::Plan(
"Unable to coerce return type of CASE expression".to_owned(),
)
},
)
}
Expr::Cast(Cast { data_type, .. })
| Expr::TryCast(TryCast { data_type, .. }) => Ok(data_type.clone()),
Expr::ScalarUDF { fun, args } => {
Expand Down Expand Up @@ -289,9 +308,9 @@ impl ExprSchemable for Expr {
#[cfg(test)]
mod tests {
use super::*;
use crate::{col, lit};
use crate::{col, lit, when};
use arrow::datatypes::DataType;
use datafusion_common::Column;
use datafusion_common::{Column, ScalarValue};

#[test]
fn expr_schema_nullability() {
Expand All @@ -312,6 +331,31 @@ mod tests {
);
}

#[test]
fn case_expr_data_type() {
let expr_else_null = when(col("foo").eq(lit(1)), lit(1_i32))
.otherwise(lit(ScalarValue::Null))
.unwrap();

assert_eq!(
DataType::Int32,
expr_else_null
.get_type(&MockExprSchema::new().with_data_type(DataType::Int64))
.unwrap()
);

let expr_then_null = when(col("foo").eq(lit(1)), lit(ScalarValue::Null))
.otherwise(lit(1_i32))
.unwrap();

assert_eq!(
DataType::Int32,
expr_then_null
.get_type(&MockExprSchema::new().with_data_type(DataType::Int64))
.unwrap()
);
}

struct MockExprSchema {
nullable: bool,
data_type: DataType,
Expand Down