clean up the codes

expression/util.go

@@ -528,13 +528,9 @@ func GetParamExpression(ctx sessionctx.Context, v *driver.ParamMarkerExpr) (Expr
 	return value, nil
 }
 
-// ConvertToByItemExpr rewrites ByItem.ExprNode to a proper ExprNode.
-func ConvertToByItemExpr(n ast.Node) ast.Node {
-	switch v := n.(type) {
-	case *driver.ParamMarkerExpr:
-		return &ast.PositionExpr{P: v}
-	}
-	return n
+// ConstructPositionExpr constructs PositionExpr with the given ParamMarkerExpr.
+func ConstructPositionExpr(p *driver.ParamMarkerExpr) *ast.PositionExpr {
+	return &ast.PositionExpr{P: p}
 }
 
 // PosFromPositionExpr generates a position value from PositionExpr.

planner/core/logical_plan_builder.go

@@ -822,9 +822,9 @@ type itemTransformer struct {
 }
 
 func (t *itemTransformer) Enter(inNode ast.Node) (ast.Node, bool) {
-	switch inNode.(type) {
+	switch n := inNode.(type) {
 	case *driver.ParamMarkerExpr:
-		newNode := expression.ConvertToByItemExpr(inNode)
+		newNode := expression.ConstructPositionExpr(n)
 		return newNode, true
 	}
 	return inNode, false
@@ -1200,11 +1200,11 @@ type gbyResolver struct {
 }
 
 func (g *gbyResolver) Enter(inNode ast.Node) (ast.Node, bool) {
-	switch inNode.(type) {
+	switch n := inNode.(type) {
 	case *ast.SubqueryExpr, *ast.CompareSubqueryExpr, *ast.ExistsSubqueryExpr:
 		return inNode, true
 	case *driver.ParamMarkerExpr:
-		newNode := expression.ConvertToByItemExpr(inNode)
+		newNode := expression.ConstructPositionExpr(n)
 		g.isParam = true
 		return newNode, true
 	case *driver.ValueExpr, *ast.ColumnNameExpr, *ast.ParenthesesExpr, *ast.ColumnName: