executor: set the correct stmtCtx for explain statement

executor/executor.go

@@ -1386,13 +1386,19 @@ func ResetContextOfStmt(ctx sessionctx.Context, s ast.StmtNode) (err error) {
 		action.SetLogHook(domain.GetDomain(ctx).ExpensiveQueryHandle().LogOnQueryExceedMemQuota)
 		sc.MemTracker.SetActionOnExceed(action)
 	}
-
 	if execStmt, ok := s.(*ast.ExecuteStmt); ok {
 		s, err = getPreparedStmt(execStmt, vars)
 		if err != nil {
 			return
 		}
 	}
+	// execute missed stmtID uses empty sql
+	sc.OriginalSQL = s.Text()
+	if explainStmt, ok := s.(*ast.ExplainStmt); ok {
+		sc.InExplainStmt = true
+		sc.CastStrToIntStrict = true
+		s = explainStmt.Stmt
+	}
 	// TODO: Many same bool variables here.
 	// We should set only two variables (
 	// IgnoreErr and StrictSQLMode) to avoid setting the same bool variables and
@@ -1454,9 +1460,6 @@ func ResetContextOfStmt(ctx sessionctx.Context, s ast.StmtNode) (err error) {
 		}
 		sc.PadCharToFullLength = ctx.GetSessionVars().SQLMode.HasPadCharToFullLengthMode()
 		sc.CastStrToIntStrict = true
-	case *ast.ExplainStmt:
-		sc.InExplainStmt = true
-		sc.CastStrToIntStrict = true
 	case *ast.ShowStmt:
 		sc.IgnoreTruncate = true
 		sc.IgnoreZeroInDate = true
@@ -1500,8 +1503,6 @@ func ResetContextOfStmt(ctx sessionctx.Context, s ast.StmtNode) (err error) {
 	if err != nil {
 		return err
 	}
-	// execute missed stmtID uses empty sql
-	sc.OriginalSQL = s.Text()
 	vars.StmtCtx = sc
 	return
 }

executor/explainfor_test.go

@@ -79,3 +79,23 @@ func (s *testSuite) TestExplainFor(c *C) {
 	tkRoot.Se.SetSessionManager(&mockSessionManager1{PS: ps})
 	tkRoot.MustExec(fmt.Sprintf("explain for connection %d", tkRootProcess.ID))
 }
+
+func (s *testSuite) TestIssue11124(c *C) {
+	tk := testkit.NewTestKitWithInit(c, s.store)
+	tk2 := testkit.NewTestKitWithInit(c, s.store)
+	tk.MustExec("create table kankan1(id int, name text);")
+	tk.MustExec("create table kankan2(id int, h1 text);")
+	tk.MustExec("insert into kankan1 values(1, 'a'), (2, 'a');")
+	tk.MustExec("insert into kankan2 values(2, 'z');")
+	tk.MustQuery("select t1.id from kankan1 t1 left join kankan2 t2 on t1.id = t2.id where (case  when t1.name='b' then 'case2' when t1.name='a' then 'case1' else NULL end) = 'case1'")
+	tkRootProcess := tk.Se.ShowProcess()
+	ps := []*util.ProcessInfo{tkRootProcess}
+	tk.Se.SetSessionManager(&mockSessionManager1{PS: ps})
+	tk2.Se.SetSessionManager(&mockSessionManager1{PS: ps})
+
+	rs := tk.MustQuery("explain select t1.id from kankan1 t1 left join kankan2 t2 on t1.id = t2.id where (case  when t1.name='b' then 'case2' when t1.name='a' then 'case1' else NULL end) = 'case1'").Rows()
+	rs2 := tk2.MustQuery(fmt.Sprintf("explain for connection %d", tkRootProcess.ID)).Rows()
+	for i := range rs {
+		c.Assert(rs[i], DeepEquals, rs2[i])
+	}
+}

executor/point_get_test.go

@@ -272,7 +272,7 @@ func (s *testPointGetSuite) TestIndexLookupChar(c *C) {
 	// Test truncate with sql mode `PAD_CHAR_TO_FULL_LENGTH`.
 	tk.MustExec(`set @@sql_mode="PAD_CHAR_TO_FULL_LENGTH";`)
 	tk.MustIndexLookup(`select * from t where a = "aa";`).Check(testkit.Rows(`aa bb`))
-	tk.MustIndexLookup(`select * from t where a = "aab";`).Check(testkit.Rows())
+	tk.MustTableDual(`select * from t where a = "aab";`).Check(testkit.Rows())
 
 	tk.MustExec(`truncate table t;`)
 	tk.MustExec(`insert into t values("a ", "b ");`)
@@ -285,9 +285,9 @@ func (s *testPointGetSuite) TestIndexLookupChar(c *C) {
 
 	// Test trailing spaces with sql mode `PAD_CHAR_TO_FULL_LENGTH`.
 	tk.MustExec(`set @@sql_mode="PAD_CHAR_TO_FULL_LENGTH";`)
-	tk.MustIndexLookup(`select * from t where a = "a";`).Check(testkit.Rows())
+	tk.MustTableDual(`select * from t where a = "a";`).Check(testkit.Rows())
 	tk.MustIndexLookup(`select * from t where a = "a ";`).Check(testkit.Rows(`a b`))
-	tk.MustIndexLookup(`select * from t where a = "a  ";`).Check(testkit.Rows())
+	tk.MustTableDual(`select * from t where a = "a  ";`).Check(testkit.Rows())
 
 	// Test CHAR BINARY.
 	tk.MustExec(`drop table if exists t;`)

util/testkit/testkit.go

@@ -199,6 +199,20 @@ func (tk *TestKit) MustIndexLookup(sql string, args ...interface{}) *Result {
 	return tk.MustQuery(sql, args...)
 }
 
+// MustTableDual checks whether the plan for the sql is TableDual.
+func (tk *TestKit) MustTableDual(sql string, args ...interface{}) *Result {
+	rs := tk.MustQuery("explain "+sql, args...)
+	hasTableDual := false
+	for i := range rs.rows {
+		if strings.Contains(rs.rows[i][0], "TableDual") {
+			hasTableDual = true
+			break
+		}
+	}
+	tk.c.Assert(hasTableDual, check.IsTrue)
+	return tk.MustQuery(sql, args...)
+}
+
 // MustPointGet checks whether the plan for the sql is Point_Get.
 func (tk *TestKit) MustPointGet(sql string, args ...interface{}) *Result {
 	rs := tk.MustQuery("explain "+sql, args...)