Preserve the Cast expression in columnize_expr

datafusion/core/tests/sql/cast.rs

@@ -26,6 +26,13 @@ async fn execute_sql(sql: &str) -> Vec<RecordBatch> {
     execute_to_batches(&ctx, sql).await
 }
 
+#[tokio::test]
+async fn cast_from_subquery() -> Result<()> {
+    let actual = execute_sql("SELECT cast(c as varchar) FROM (SELECT 1 as c)").await;
+    assert_eq!(&DataType::Utf8, actual[0].schema().field(0).data_type());
+    Ok(())
+}
+
 #[tokio::test]
 async fn cast_tinyint() -> Result<()> {
     let actual = execute_sql("SELECT cast(10 as tinyint)").await;

datafusion/expr/src/utils.rs

@@ -25,7 +25,7 @@ use crate::logical_plan::{
     Limit, Partitioning, Projection, Repartition, Sort, Subquery, SubqueryAlias, Union,
     Values, Window,
 };
-use crate::{Expr, ExprSchemable, LogicalPlan, LogicalPlanBuilder};
+use crate::{Cast, Expr, ExprSchemable, LogicalPlan, LogicalPlanBuilder};
 use arrow::datatypes::{DataType, TimeUnit};
 use datafusion_common::{
     Column, DFField, DFSchema, DFSchemaRef, DataFusionError, Result, ScalarValue,
@@ -676,6 +676,10 @@ pub fn columnize_expr(e: Expr, input_schema: &DFSchema) -> Expr {
         Expr::Alias(inner_expr, name) => {
             Expr::Alias(Box::new(columnize_expr(*inner_expr, input_schema)), name)
         }
+        Expr::Cast(Cast { expr, data_type }) => Expr::Cast(Cast {
+            expr: Box::new(columnize_expr(*expr, input_schema)),
+            data_type,
+        }),
         Expr::ScalarSubquery(_) => e.clone(),
         _ => match e.display_name() {
             Ok(name) => match input_schema.field_with_unqualified_name(&name) {

datafusion/sql/src/planner.rs

@@ -2974,6 +2974,17 @@ mod tests {
         );
     }
 
+    #[test]
+    fn cast_from_subquery() {
+        quick_test(
+            "SELECT CAST (a AS FLOAT) FROM (SELECT 1 AS a)",
+            "Projection: CAST(a AS Float32)\
+             \n  Projection: a\
+             \n    Projection: Int64(1) AS a\
+             \n      EmptyRelation",
+        );
+    }
+
     #[test]
     fn cast_to_invalid_decimal_type() {
         // precision == 0