fix: preserve qualifiers when rewriting expressions

datafusion/expr/src/expr.rs

@@ -227,7 +227,7 @@ use sqlparser::ast::{
 pub enum Expr {
     /// An expression with a specific name.
     Alias(Alias),
-    /// A named reference to a qualified filed in a schema.
+    /// A named reference to a qualified field in a schema.
     Column(Column),
     /// A named reference to a variable in a registry.
     ScalarVariable(DataType, Vec<String>),
@@ -1115,6 +1115,19 @@ impl Expr {
         SchemaDisplay(self)
     }
 
+    /// Returns the qualifier and the schema name of this expression.
+    ///
+    /// Used when the expression forms the output field of a certain plan.
+    /// The result is the field's qualifier and field name in the plan's
+    /// output schema. We can use this qualified name to reference the field.
+    pub fn qualified_name(&self) -> (Option<TableReference>, String) {
+        match self {
+            Expr::Column(Column { relation, name }) => (relation.clone(), name.clone()),
+            Expr::Alias(Alias { relation, name, .. }) => (relation.clone(), name.clone()),
+            _ => (None, self.schema_name().to_string()),
+        }
+    }
+
     /// Returns a full and complete string representation of this expression.
     #[deprecated(note = "use format! instead")]
     pub fn canonical_name(&self) -> String {

datafusion/expr/src/expr_rewriter/mod.rs

@@ -26,9 +26,7 @@ use crate::logical_plan::Projection;
 use crate::{Expr, ExprSchemable, LogicalPlan, LogicalPlanBuilder};
 
 use datafusion_common::config::ConfigOptions;
-use datafusion_common::tree_node::{
-    Transformed, TransformedResult, TreeNode, TreeNodeRewriter,
-};
+use datafusion_common::tree_node::{Transformed, TransformedResult, TreeNode};
 use datafusion_common::TableReference;
 use datafusion_common::{Column, DFSchema, Result};
 
@@ -279,22 +277,10 @@ pub fn unalias(expr: Expr) -> Expr {
     }
 }
 
-/// Rewrites `expr` using `rewriter`, ensuring that the output has the
-/// same name as `expr` prior to rewrite, adding an alias if necessary.
-///
-/// This is important when optimizing plans to ensure the output
-/// schema of plan nodes don't change after optimization
-pub fn rewrite_preserving_name<R>(expr: Expr, rewriter: &mut R) -> Result<Expr>
-where
-    R: TreeNodeRewriter<Node = Expr>,
-{
-    let original_name = expr.name_for_alias()?;
-    let expr = expr.rewrite(rewriter)?.data;
-    expr.alias_if_changed(original_name)
-}
-
 /// Handles ensuring the name of rewritten expressions is not changed.
 ///
+/// This is important when optimizing plans to ensure the output
+/// schema of plan nodes don't change after optimization.
 /// For example, if an expression `1 + 2` is rewritten to `3`, the name of the
 /// expression should be preserved: `3 as "1 + 2"`
 ///
@@ -303,9 +289,17 @@ pub struct NamePreserver {
     use_alias: bool,
 }
 
-/// If the name of an expression is remembered, it will be preserved when
-/// rewriting the expression
-pub struct SavedName(Option<String>);
+/// If the qualified name of an expression is remembered, it will be preserved
+/// when rewriting the expression
+pub enum SavedName {
+    /// Saved qualified name to be preserved
+    Saved {
+        relation: Option<TableReference>,
+        name: String,
+    },
+    /// Name is not preserved
+    None,
+}
 
 impl NamePreserver {
     /// Create a new NamePreserver for rewriting the `expr` that is part of the specified plan
@@ -326,23 +320,30 @@ impl NamePreserver {
 
     pub fn save(&self, expr: &Expr) -> Result<SavedName> {
         let original_name = if self.use_alias {
-            Some(expr.name_for_alias()?)
+            let (relation, name) = expr.qualified_name();
+            SavedName::Saved { relation, name }
         } else {
-            None
+            SavedName::None
         };
-
-        Ok(SavedName(original_name))
+        Ok(original_name)
     }
 }
 
 impl SavedName {
-    /// Ensures the name of the rewritten expression is preserved
+    /// Ensures the qualified name of the rewritten expression is preserved
     pub fn restore(self, expr: Expr) -> Result<Expr> {
-        let Self(original_name) = self;
-        match original_name {
-            Some(name) => expr.alias_if_changed(name),
-            None => Ok(expr),
-        }
+        let expr = match self {
+            SavedName::Saved { relation, name } => {
+                let (new_relation, new_name) = expr.qualified_name();
+                if new_relation != relation || new_name != name {
+                    expr.alias_qualified(relation, name)
+                } else {
+                    expr
+                }
+            }
+            SavedName::None => expr,
+        };
+        Ok(expr)
     }
 }
 
@@ -353,6 +354,7 @@ mod test {
     use super::*;
     use crate::{col, lit, Cast};
     use arrow::datatypes::{DataType, Field, Schema};
+    use datafusion_common::tree_node::TreeNodeRewriter;
     use datafusion_common::ScalarValue;
 
     #[derive(Default)]
@@ -511,10 +513,20 @@ mod test {
 
         // change literal type from i32 to i64
         test_rewrite(col("a").add(lit(1i32)), col("a").add(lit(1i64)));
+
+        // test preserve qualifier
+        test_rewrite(
+            Expr::Column(Column::new(Some("test"), "a")),
+            Expr::Column(Column::new_unqualified("test.a")),
+        );
+        test_rewrite(
+            Expr::Column(Column::new_unqualified("test.a")),
+            Expr::Column(Column::new(Some("test"), "a")),
+        );
     }
 
-    /// rewrites `expr_from` to `rewrite_to` using
-    /// `rewrite_preserving_name` verifying the result is `expected_expr`
+    /// rewrites `expr_from` to `rewrite_to` while preserving the original qualified name
+    /// by using the `NamePreserver`
     fn test_rewrite(expr_from: Expr, rewrite_to: Expr) {
         struct TestRewriter {
             rewrite_to: Expr,
@@ -531,11 +543,12 @@ mod test {
         let mut rewriter = TestRewriter {
             rewrite_to: rewrite_to.clone(),
         };
-        let expr = rewrite_preserving_name(expr_from.clone(), &mut rewriter).unwrap();
-
-        let original_name = expr_from.schema_name().to_string();
-        let new_name = expr.schema_name().to_string();
+        let saved_name = NamePreserver { use_alias: true }.save(&expr_from).unwrap();
+        let new_expr = expr_from.clone().rewrite(&mut rewriter).unwrap().data;
+        let new_expr = saved_name.restore(new_expr).unwrap();
 
+        let original_name = expr_from.qualified_name();
+        let new_name = new_expr.qualified_name();
         assert_eq!(
             original_name, new_name,
             "mismatch rewriting expr_from: {expr_from} to {rewrite_to}"

datafusion/expr/src/expr_schema.rs

@@ -462,35 +462,12 @@ impl ExprSchemable for Expr {
         &self,
         input_schema: &dyn ExprSchema,
     ) -> Result<(Option<TableReference>, Arc<Field>)> {
-        match self {
-            Expr::Column(c) => {
-                let (data_type, nullable) = self.data_type_and_nullable(input_schema)?;
-                Ok((
-                    c.relation.clone(),
-                    Field::new(&c.name, data_type, nullable)
-                        .with_metadata(self.metadata(input_schema)?)
-                        .into(),
-                ))
-            }
-            Expr::Alias(Alias { relation, name, .. }) => {
-                let (data_type, nullable) = self.data_type_and_nullable(input_schema)?;
-                Ok((
-                    relation.clone(),
-                    Field::new(name, data_type, nullable)
-                        .with_metadata(self.metadata(input_schema)?)
-                        .into(),
-                ))
-            }
-            _ => {
-                let (data_type, nullable) = self.data_type_and_nullable(input_schema)?;
-                Ok((
-                    None,
-                    Field::new(self.schema_name().to_string(), data_type, nullable)
-                        .with_metadata(self.metadata(input_schema)?)
-                        .into(),
-                ))
-            }
-        }
+        let (relation, schema_name) = self.qualified_name();
+        let (data_type, nullable) = self.data_type_and_nullable(input_schema)?;
+        let field = Field::new(schema_name, data_type, nullable)
+            .with_metadata(self.metadata(input_schema)?)
+            .into();
+        Ok((relation, field))
     }
 
     /// Wraps this expression in a cast to a target [arrow::datatypes::DataType].

datafusion/sqllogictest/test_files/select.slt

@@ -1685,6 +1685,9 @@ SELECT i + i FROM test WHERE i > 2;
 ----
 6
 
+statement ok
+DROP TABLE test;
+
 query error DataFusion error: Arrow error: Parser error: Error parsing timestamp from 'I AM NOT A TIMESTAMP': error parsing date
 SELECT to_timestamp('I AM NOT A TIMESTAMP');
 
@@ -1741,3 +1744,15 @@ select a from t;
 
 statement ok
 set datafusion.optimizer.max_passes=3;
+
+# Test issue: https://github.com/apache/datafusion/issues/12183
+statement ok
+CREATE TABLE test(a BIGINT) AS VALUES (1);
+
+query I
+SELECT "test.a" FROM (SELECT a AS "test.a" FROM test)
+----
+1
+
+statement ok
+DROP TABLE test;