Infer placeholder datatype for Expr::InSubquery (#80)

* infer placeholder datatype for InSubquery

* update comment

* only infer subquery if exactly 1 field

Author: kczimm

datafusion/expr/src/expr.rs

@@ -1623,6 +1623,26 @@ impl Expr {
                 | Expr::SimilarTo(Like { expr, pattern, .. }) => {
                     rewrite_placeholder(pattern.as_mut(), expr.as_ref(), schema)?;
                 }
+                Expr::InSubquery(InSubquery {
+                    expr,
+                    subquery,
+                    negated: _,
+                }) => {
+                    let subquery_schema = subquery.subquery.schema();
+                    let fields = subquery_schema.fields();
+
+                    // only supports subquery with exactly 1 field
+                    if let [first_field] = &fields[..] {
+                        rewrite_placeholder(
+                            expr.as_mut(),
+                            &Expr::Column(Column {
+                                relation: None,
+                                name: first_field.name().clone(),
+                            }),
+                            schema,
+                        )?;
+                    }
+                }
                 Expr::Placeholder(_) => {
                     has_placeholder = true;
                 }
@@ -2801,7 +2821,8 @@ mod test {
     use crate::expr_fn::col;
     use crate::{
         case, lit, qualified_wildcard, wildcard, wildcard_with_options, ColumnarValue,
-        ScalarFunctionArgs, ScalarUDF, ScalarUDFImpl, Volatility,
+        LogicalPlan, LogicalTableSource, Projection, ScalarFunctionArgs, ScalarUDF,
+        ScalarUDFImpl, TableScan, Volatility,
     };
     use arrow::datatypes::{Field, Schema};
     use sqlparser::ast;
@@ -2863,6 +2884,86 @@ mod test {
         }
     }
 
+    #[test]
+    fn infer_placeholder_in_subquery() -> Result<()> {
+        // Schema for my_table: A (Int32), B (Int32)
+        let schema = Arc::new(Schema::new(vec![
+            Field::new("A", DataType::Int32, true),
+            Field::new("B", DataType::Int32, true),
+        ]));
+
+        let source = Arc::new(LogicalTableSource::new(schema.clone()));
+
+        // Simulate: SELECT * FROM my_table WHERE $1 IN (SELECT A FROM my_table WHERE B > 3);
+        let placeholder = Expr::Placeholder(Placeholder {
+            id: "$1".to_string(),
+            data_type: None,
+        });
+
+        // Subquery: SELECT A FROM my_table WHERE B > 3
+        let subquery_filter = Expr::BinaryExpr(BinaryExpr {
+            left: Box::new(col("B")),
+            op: Operator::Gt,
+            right: Box::new(Expr::Literal(ScalarValue::Int32(Some(3)))),
+        });
+
+        let subquery_scan = LogicalPlan::TableScan(TableScan {
+            table_name: TableReference::from("my_table"),
+            source,
+            projected_schema: Arc::new(DFSchema::try_from(schema.clone())?),
+            projection: None,
+            filters: vec![subquery_filter.clone()],
+            fetch: None,
+        });
+
+        let projected_fields = vec![Field::new("A", DataType::Int32, true)];
+        let projected_schema = Arc::new(DFSchema::from_unqualified_fields(
+            projected_fields.into(),
+            Default::default(),
+        )?);
+
+        let subquery = Subquery {
+            subquery: Arc::new(LogicalPlan::Projection(Projection {
+                expr: vec![col("A")],
+                input: Arc::new(subquery_scan),
+                schema: projected_schema,
+            })),
+            outer_ref_columns: vec![],
+        };
+
+        let in_subquery = Expr::InSubquery(InSubquery {
+            expr: Box::new(placeholder),
+            subquery,
+            negated: false,
+        });
+
+        let df_schema = DFSchema::try_from(schema)?;
+
+        let (inferred_expr, contains_placeholder) =
+            in_subquery.infer_placeholder_types(&df_schema)?;
+
+        assert!(
+            contains_placeholder,
+            "Expression should contain a placeholder"
+        );
+
+        match inferred_expr {
+            Expr::InSubquery(in_subquery) => match *in_subquery.expr {
+                Expr::Placeholder(placeholder) => {
+                    assert_eq!(
+                        placeholder.data_type,
+                        Some(DataType::Int32),
+                        "Placeholder $1 should infer Int32"
+                    );
+                }
+                _ => panic!("Expected Placeholder expression in InSubquery"),
+            },
+            _ => panic!("Expected InSubquery expression"),
+        }
+
+        Ok(())
+    }
+
     #[test]
     fn infer_placeholder_like_and_similar_to() {
         // name LIKE $1