plan :fix the compatibility problem of UNION statement

executor/executor_test.go

@@ -947,8 +947,17 @@ func (s *testSuite) TestUnion(c *C) {
 	tk.MustExec("create table t(a int)")
 	tk.MustExec("insert into t value(0),(0)")
 	tk.MustQuery("select 1 from (select a from t union all select a from t) tmp").Check(testkit.Rows("1", "1", "1", "1"))
-	tk.MustQuery("select 1 from (select a from t limit 1 union all select a from t limit 1) tmp").Check(testkit.Rows("1", "1"))
 	tk.MustQuery("select count(1) from (select a from t union all select a from t) tmp").Check(testkit.Rows("4"))
+
+	_, err := tk.Exec("select 1 from (select a from t limit 1 union all select a from t limit 1) tmp")
+	c.Assert(err, NotNil)
+	terr := errors.Trace(err).(*errors.Err).Cause().(*terror.Error)
+	c.Assert(terr.Code(), Equals, terror.ErrCode(mysql.ErrWrongUsage))
+
+	_, err = tk.Exec("select 1 from (select a from t order by a union all select a from t limit 1) tmp")
+	c.Assert(err, NotNil)
+	terr = errors.Trace(err).(*errors.Err).Cause().(*terror.Error)
+	c.Assert(terr.Code(), Equals, terror.ErrCode(mysql.ErrWrongUsage))
 }
 
 func (s *testSuite) TestIn(c *C) {

plan/errors.go

@@ -0,0 +1,35 @@
+// Copyright 2018 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package plan
+
+import (
+	"github.com/pingcap/tidb/mysql"
+	"github.com/pingcap/tidb/terror"
+)
+
+var (
+	// ErrWrongUsage is returned when SQL operators are not properly used.
+	ErrWrongUsage = terror.ClassParser.New(codeWrongUsage, mysql.MySQLErrName[mysql.ErrWrongUsage])
+)
+
+const (
+	codeWrongUsage = terror.ErrCode(mysql.ErrWrongUsage)
+)
+
+func init() {
+	typesMySQLErrCodes := map[terror.ErrCode]uint16{
+		codeWrongUsage: mysql.ErrWrongUsage,
+	}
+	terror.ErrClassToMySQLCodes[terror.ClassParser] = typesMySQLErrCodes
+}

plan/preprocess.go

@@ -68,6 +68,8 @@ func (p *preprocessor) Enter(in ast.Node) (out ast.Node, skipChildren bool) {
 		p.checkDropDatabaseGrammar(node)
 	case *ast.ShowStmt:
 		p.resolveShowStmt(node)
+	case *ast.UnionSelectList:
+		p.checkUnionSelectList(node)
 	case *ast.DeleteTableList:
 		return in, true
 	}
@@ -205,6 +207,18 @@ func (p *preprocessor) checkAutoIncrement(stmt *ast.CreateTableStmt) {
 	}
 }
 
+func (p *preprocessor) checkUnionSelectList(stmt *ast.UnionSelectList) {
+	for idx, sel := range stmt.Selects {
+		if idx != len(stmt.Selects)-1 {
+			if sel.OrderBy != nil {
+				p.err = ErrWrongUsage.GenByArgs("UNION", "ORDER BY")
+			} else if sel.Limit != nil {
+				p.err = ErrWrongUsage.GenByArgs("UNION", "LIMIT")
+			}
+		}
+	}
+}
+
 func (p *preprocessor) checkCreateDatabaseGrammar(stmt *ast.CreateDatabaseStmt) {
 	if isIncorrectName(stmt.Name) {
 		p.err = ddl.ErrWrongDBName.GenByArgs(stmt.Name)