check variable starts with '@' for select expression assignment

go/vt/sqlparser/ast.go

@@ -4745,6 +4745,7 @@ func (*ConvertUsingExpr) iExpr()  {}
 func (*MatchExpr) iExpr()         {}
 func (*GroupConcatExpr) iExpr()   {}
 func (*Default) iExpr()           {}
+func (*SetVarExpr) iExpr()        {}
 
 // ReplaceExpr finds the from expression from root
 // and replaces it with to. If from matches root,
@@ -6661,6 +6662,10 @@ func (node *SetVarExpr) walkSubtree(visit Visit) error {
 	)
 }
 
+func (node *SetVarExpr) replace(from, to Expr) bool {
+	return false
+}
+
 // OnDup represents an ON DUPLICATE KEY clause.
 type OnDup AssignmentExprs
 

go/vt/sqlparser/parse_test.go

@@ -3235,6 +3235,9 @@ var (
 		}, {
 			input:  "ALTER TABLE webhook_events ADD COLUMN event varchar(255) DEFAULT NULL;",
 			output: "alter table webhook_events add column (\n\t`event` varchar(255) default null\n)",
+		}, {
+			input:  "select @id := 1",
+			output: "select @id = 1",
 		},
 		// Create Spatial Reference System Statements
 		{
@@ -6783,6 +6786,9 @@ var (
 	}, {
 		input:  "ALTER DEFINER = `newuser`@`localhost` EVENT myevent",
 		output: "You have an error in your SQL syntax; At least one event field to alter needs to be defined at position 52 near 'myevent'",
+	}, {
+		input:  "select id := 1",
+		output: "syntax error at position 15 near '1'",
 	},
 	}