parser: disallow subquery without table alias (#19102)

ddl/error.go

@@ -191,6 +191,8 @@ var (
 	ErrFunctionalIndexOnField = terror.ClassDDL.New(mysql.ErrFunctionalIndexOnField, mysql.MySQLErrName[mysql.ErrFunctionalIndexOnField])
 	// ErrInvalidAutoRandom returns when auto_random is used incorrectly.
 	ErrInvalidAutoRandom = terror.ClassDDL.New(mysql.ErrInvalidAutoRandom, mysql.MySQLErrName[mysql.ErrInvalidAutoRandom])
+	// ErrDerivedMustHaveAlias returns when a sub select statement does not have a table alias.
+	ErrDerivedMustHaveAlias = terror.ClassDDL.New(mysql.ErrDerivedMustHaveAlias, mysql.MySQLErrName[mysql.ErrDerivedMustHaveAlias])
 
 	// ErrSequenceRunOut returns when the sequence has been run out.
 	ErrSequenceRunOut = terror.ClassDDL.New(mysql.ErrSequenceRunOut, mysql.MySQLErrName[mysql.ErrSequenceRunOut])

errors.toml

@@ -121,6 +121,11 @@ error = '''
 The used table type doesn't support FULLTEXT indexes
 '''
 
+["ddl:1248"]
+error = '''
+Every derived table must have its own alias
+'''
+
 ["ddl:1253"]
 error = '''
 COLLATION '%s' is not valid for CHARACTER SET '%s'

executor/executor_test.go

@@ -3916,7 +3916,33 @@ func (s *testSuite3) TestDoSubquery(c *C) {
 	c.Assert(r, IsNil, Commentf("result of Do not empty"))
 }
 
-func (s *testSuite3) TestTSOFail(c *C) {
+func (s *testSuite3) TestSubqueryTableAlias(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec(`use test`)
+	tk.MustExec(`drop table if exists t`)
+
+	tk.MustExec("set sql_mode = ''")
+	tk.MustGetErrCode("select a, b from (select 1 a) ``, (select 2 b) ``;", mysql.ErrDerivedMustHaveAlias)
+	tk.MustGetErrCode("select a, b from (select 1 a) `x`, (select 2 b) `x`;", mysql.ErrNonuniqTable)
+	tk.MustGetErrCode("select a, b from (select 1 a), (select 2 b);", mysql.ErrDerivedMustHaveAlias)
+	// ambiguous column name
+	tk.MustGetErrCode("select a from (select 1 a) ``, (select 2 a) ``;", mysql.ErrDerivedMustHaveAlias)
+	tk.MustGetErrCode("select a from (select 1 a) `x`, (select 2 a) `x`;", mysql.ErrNonuniqTable)
+	tk.MustGetErrCode("select x.a from (select 1 a) `x`, (select 2 a) `x`;", mysql.ErrNonuniqTable)
+	tk.MustGetErrCode("select a from (select 1 a), (select 2 a);", mysql.ErrDerivedMustHaveAlias)
+
+	tk.MustExec("set sql_mode = 'oracle';")
+	tk.MustQuery("select a, b from (select 1 a) ``, (select 2 b) ``;").Check(testkit.Rows("1 2"))
+	tk.MustQuery("select a, b from (select 1 a) `x`, (select 2 b) `x`;").Check(testkit.Rows("1 2"))
+	tk.MustQuery("select a, b from (select 1 a), (select 2 b);").Check(testkit.Rows("1 2"))
+	// ambiguous column name
+	tk.MustGetErrCode("select a from (select 1 a) ``, (select 2 a) ``;", mysql.ErrNonUniq)
+	tk.MustGetErrCode("select a from (select 1 a) `x`, (select 2 a) `x`;", mysql.ErrNonUniq)
+	tk.MustGetErrCode("select x.a from (select 1 a) `x`, (select 2 a) `x`;", mysql.ErrNonUniq)
+	tk.MustGetErrCode("select a from (select 1 a), (select 2 a);", mysql.ErrNonUniq)
+}
+
+func (s *testSerialSuite1) TestTSOFail(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec(`use test`)
 	tk.MustExec(`drop table if exists t`)

planner/core/preprocess.go

@@ -188,6 +188,11 @@ func (p *preprocessor) Enter(in ast.Node) (out ast.Node, skipChildren bool) {
 		if node.Kind == ast.BRIEKindRestore {
 			p.flag |= inCreateOrDropTable
 		}
+	case *ast.TableSource:
+		isModeOracle := p.ctx.GetSessionVars().SQLMode&mysql.ModeOracle != 0
+		if _, ok := node.Source.(*ast.SelectStmt); ok && !isModeOracle && len(node.AsName.L) == 0 {
+			p.err = ddl.ErrDerivedMustHaveAlias.GenWithStackByArgs()
+		}
 	default:
 		p.flag &= ^parentIsJoin
 	}
@@ -556,13 +561,16 @@ func (p *preprocessor) checkNonUniqTableAlias(stmt *ast.Join) {
 		p.tableAliasInJoin = append(p.tableAliasInJoin, make(map[string]interface{}))
 	}
 	tableAliases := p.tableAliasInJoin[len(p.tableAliasInJoin)-1]
-	if err := isTableAliasDuplicate(stmt.Left, tableAliases); err != nil {
-		p.err = err
-		return
-	}
-	if err := isTableAliasDuplicate(stmt.Right, tableAliases); err != nil {
-		p.err = err
-		return
+	isOracleMode := p.ctx.GetSessionVars().SQLMode&mysql.ModeOracle != 0
+	if !isOracleMode {
+		if err := isTableAliasDuplicate(stmt.Left, tableAliases); err != nil {
+			p.err = err
+			return
+		}
+		if err := isTableAliasDuplicate(stmt.Right, tableAliases); err != nil {
+			p.err = err
+			return
+		}
 	}
 	p.flag |= parentIsJoin
 }