planner: correct the generation of the field name (#11324) (#11379)

executor/executor_test.go

@@ -2115,6 +2115,13 @@ func (s *testSuite) TestColumnName(c *C) {
 	c.Assert(fields[1].ColumnAsName.L, Equals, "num")
 	tk.MustExec("set @@tidb_enable_window_function = 0")
 	rs.Close()
+
+	rs, err = tk.Exec("select if(1,c,c) from t;")
+	c.Check(err, IsNil)
+	fields = rs.Fields()
+	c.Assert(fields[0].Column.Name.L, Equals, "if(1,c,c)")
+	// It's a compatibility issue. Should be empty instead.
+	c.Assert(fields[0].ColumnAsName.L, Equals, "if(1,c,c)")
 }
 
 func (s *testSuite) TestSelectVar(c *C) {

planner/core/logical_plan_builder.go

@@ -600,12 +600,10 @@ func (b *PlanBuilder) buildSelection(p LogicalPlan, where ast.ExprNode, AggMappe
 }
 
 // buildProjectionFieldNameFromColumns builds the field name, table name and database name when field expression is a column reference.
-func (b *PlanBuilder) buildProjectionFieldNameFromColumns(field *ast.SelectField, c *expression.Column) (colName, origColName, tblName, origTblName, dbName model.CIStr) {
-	if astCol, ok := getInnerFromParenthesesAndUnaryPlus(field.Expr).(*ast.ColumnNameExpr); ok {
-		origColName, tblName, dbName = astCol.Name.Name, astCol.Name.Table, astCol.Name.Schema
-	}
-	if field.AsName.L != "" {
-		colName = field.AsName
+func (b *PlanBuilder) buildProjectionFieldNameFromColumns(origField *ast.SelectField, colNameField *ast.ColumnNameExpr, c *expression.Column) (colName, origColName, tblName, origTblName, dbName model.CIStr) {
+	origColName, tblName, dbName = colNameField.Name.Name, colNameField.Name.Table, colNameField.Name.Schema
+	if origField.AsName.L != "" {
+		colName = origField.AsName
 	} else {
 		colName = origColName
 	}
@@ -686,9 +684,13 @@ func (b *PlanBuilder) buildProjectionFieldNameFromExpressions(field *ast.SelectF
 // buildProjectionField builds the field object according to SelectField in projection.
 func (b *PlanBuilder) buildProjectionField(id, position int, field *ast.SelectField, expr expression.Expression) (*expression.Column, error) {
 	var origTblName, tblName, origColName, colName, dbName model.CIStr
-	if c, ok := expr.(*expression.Column); ok && !c.IsReferenced {
+	innerNode := getInnerFromParenthesesAndUnaryPlus(field.Expr)
+	col, isCol := expr.(*expression.Column)
+	// Correlated column won't affect the final output names. So we can put it in any of the three logic block.
+	// Don't put it into the first block just for simplifying the codes.
+	if colNameField, ok := innerNode.(*ast.ColumnNameExpr); ok && isCol {
 		// Field is a column reference.
-		colName, origColName, tblName, origTblName, dbName = b.buildProjectionFieldNameFromColumns(field, c)
+		colName, origColName, tblName, origTblName, dbName = b.buildProjectionFieldNameFromColumns(field, colNameField, col)
 	} else if field.AsName.L != "" {
 		// Field has alias.
 		colName = field.AsName