expression: fix wrong caseWhen function for enum type (#29454)

expression/builtin_control.go

@@ -218,6 +218,14 @@ func (c *caseWhenFunctionClass) getFunction(ctx sessionctx.Context, args []Expre
 		return nil, err
 	}
 	bf.tp = fieldTp
+	if fieldTp.Tp == mysql.TypeEnum || fieldTp.Tp == mysql.TypeSet {
+		switch tp {
+		case types.ETInt:
+			fieldTp.Tp = mysql.TypeLonglong
+		case types.ETString:
+			fieldTp.Tp = mysql.TypeVarchar
+		}
+	}
 
 	switch tp {
 	case types.ETInt:

expression/constant_fold.go

@@ -139,7 +139,7 @@ func caseWhenHandler(expr *ScalarFunction) (Expression, bool) {
 			foldedExpr.GetType().Decimal = expr.GetType().Decimal
 			return foldedExpr, isDeferredConst
 		}
-		return BuildCastFunction(expr.GetCtx(), foldedExpr, foldedExpr.GetType()), isDeferredConst
+		return foldedExpr, isDeferredConst
 	}
 	return expr, isDeferredConst
 }

expression/integration_test.go

@@ -8325,6 +8325,23 @@ func (s *testIntegrationSerialSuite) TestIssue26662(c *C) {
 		Check(testkit.Rows())
 }
 
+func (s *testIntegrationSuite) TestControlFunctionWithEnumOrSet(c *C) {
+	// issue 29357
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t;")
+	tk.MustExec("create table t(`a` enum('y','b','Abc','null','1','2','0')) CHARSET=binary;")
+	tk.MustExec("insert into t values(\"1\");")
+	tk.MustQuery("SELECT count(*) from t where (null like 'a') = (case when cast('2015' as real) <=> round(\"1200\",\"1\") then a end);\n").Check(testkit.Rows("0"))
+	tk.MustQuery("SELECT (null like 'a') = (case when cast('2015' as real) <=> round(\"1200\",\"1\") then a end) from t;\n").Check(testkit.Rows("<nil>"))
+	tk.MustQuery("SELECT 5 = (case when 0 <=> 0 then a end) from t;").Check(testkit.Rows("1"))
+	tk.MustQuery("SELECT '1' = (case when 0 <=> 0 then a end) from t;").Check(testkit.Rows("1"))
+	tk.MustQuery("SELECT 5 = (case when 0 <=> 1 then a end) from t;").Check(testkit.Rows("<nil>"))
+	tk.MustQuery("SELECT '1' = (case when 0 <=> 1 then a end) from t;").Check(testkit.Rows("<nil>"))
+	tk.MustQuery("SELECT 5 = (case when 0 <=> 1 then a else a end) from t;").Check(testkit.Rows("1"))
+	tk.MustQuery("SELECT '1' = (case when 0 <=> 1 then a else a end) from t;").Check(testkit.Rows("1"))
+}
+
 func (s *testIntegrationSuite) TestConstPropNullFunctions(c *C) {
 	tk := testkit.NewTestKit(c, s.store)
 	tk.MustExec("use test")