expression: fix issue that function dayname is incompatible with Mysql when doing arithmetic

expression/builtin_cast.go

@@ -1687,6 +1687,23 @@ func (i inCastContext) String() string {
 // @see BuildCastFunction4Union
 const inUnionCastContext inCastContext = 0
 
+// hasSpecialCast checks if this expr has its own special cast function.
+// for example(#9713): when doing arithmetic using results of function DayName,
+// "Monday" should be regarded as 0, "Tuesday" should be regarded as 1 and so on.
+func hasSpecialCast(ctx sessionctx.Context, expr Expression, tp *types.FieldType) bool {
+	switch f := expr.(type) {
+	case *ScalarFunction:
+		switch f.FuncName.L {
+		case ast.DayName:
+			switch tp.EvalType() {
+			case types.ETInt, types.ETReal:
+				return true
+			}
+		}
+	}
+	return false
+}
+
 // BuildCastFunction4Union build a implicitly CAST ScalarFunction from the Union
 // Expression.
 func BuildCastFunction4Union(ctx sessionctx.Context, expr Expression, tp *types.FieldType) (res Expression) {
@@ -1699,6 +1716,10 @@ func BuildCastFunction4Union(ctx sessionctx.Context, expr Expression, tp *types.
 
 // BuildCastFunction builds a CAST ScalarFunction from the Expression.
 func BuildCastFunction(ctx sessionctx.Context, expr Expression, tp *types.FieldType) (res Expression) {
+	if hasSpecialCast(ctx, expr, tp) {
+		return expr
+	}
+
 	var fc functionClass
 	switch tp.EvalType() {
 	case types.ETInt:

expression/builtin_time.go

@@ -1079,21 +1079,45 @@ func (b *builtinDayNameSig) Clone() builtinFunc {
 	return newSig
 }
 
-// evalString evals a builtinDayNameSig.
-// See https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_dayname
-func (b *builtinDayNameSig) evalString(row chunk.Row) (string, bool, error) {
+func (b *builtinDayNameSig) evalIndex(row chunk.Row) (int64, bool, error) {
 	arg, isNull, err := b.args[0].EvalTime(b.ctx, row)
 	if isNull || err != nil {
-		return "", isNull, err
+		return 0, isNull, err
 	}
 	if arg.InvalidZero() {
-		return "", true, handleInvalidTimeError(b.ctx, types.ErrIncorrectDatetimeValue.GenWithStackByArgs(arg.String()))
+		return 0, true, handleInvalidTimeError(b.ctx, types.ErrIncorrectDatetimeValue.GenWithStackByArgs(arg.String()))
 	}
 	// Monday is 0, ... Sunday = 6 in MySQL
 	// but in go, Sunday is 0, ... Saturday is 6
 	// w will do a conversion.
 	res := (int64(arg.Time.Weekday()) + 6) % 7
-	return types.WeekdayNames[res], false, nil
+	return res, false, nil
+}
+
+// evalString evals a builtinDayNameSig.
+// See https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_dayname
+func (b *builtinDayNameSig) evalString(row chunk.Row) (string, bool, error) {
+	idx, isNull, err := b.evalIndex(row)
+	if isNull || err != nil {
+		return "", isNull, err
+	}
+	return types.WeekdayNames[idx], false, nil
+}
+
+func (b *builtinDayNameSig) evalReal(row chunk.Row) (float64, bool, error) {
+	idx, isNull, err := b.evalIndex(row)
+	if isNull || err != nil {
+		return 0, isNull, err
+	}
+	return float64(idx), false, nil
+}
+
+func (b *builtinDayNameSig) evalInt(row chunk.Row) (int64, bool, error) {
+	idx, isNull, err := b.evalIndex(row)
+	if isNull || err != nil {
+		return 0, isNull, err
+	}
+	return idx, false, nil
 }
 
 type dayOfMonthFunctionClass struct {

expression/function_traits.go

@@ -42,6 +42,7 @@ var unFoldableFunctions = map[string]struct{}{
 	ast.GetVar:    {},
 	ast.GetParam:  {},
 	ast.Benchmark: {},
+	ast.DayName:   {},
 }
 
 // DisableFoldFunctions stores functions which prevent child scope functions from being constant folded.

expression/integration_test.go

@@ -4134,3 +4134,51 @@ func (s *testIntegrationSuite) TestDecimalConvertToTime(c *C) {
 	tk.MustExec("insert t values (20010101100000.123456, 20110707101112.123456)")
 	tk.MustQuery("select * from t").Check(testkit.Rows("2001-01-01 10:00:00.123456 2011-07-07 10:11:12"))
 }
+
+func (s *testIntegrationSuite) TestDaynameArithmetic(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	defer s.cleanEnv(c)
+
+	cases := []struct {
+		sql    string
+		result string
+	}{
+		{`select dayname("1962-03-01")+0;`, "3"},
+		{`select dayname("1962-03-02")+0;`, "4"},
+		{`select dayname("1962-03-03")+0;`, "5"},
+		{`select dayname("1962-03-04")+0;`, "6"},
+		{`select dayname("1962-03-05")+0;`, "0"},
+		{`select dayname("1962-03-06")+0;`, "1"},
+		{`select dayname("1962-03-07")+0;`, "2"},
+		{`select dayname("1962-03-08")+0;`, "3"},
+		{`select dayname("1962-03-01")+1;`, "4"},
+		{`select dayname("1962-03-01")+2;`, "5"},
+		{`select dayname("1962-03-01")+3;`, "6"},
+		{`select dayname("1962-03-01")+4;`, "7"},
+		{`select dayname("1962-03-01")+5;`, "8"},
+		{`select dayname("1962-03-01")+6;`, "9"},
+		{`select dayname("1962-03-01")+7;`, "10"},
+		{`select dayname("1962-03-01")+2333;`, "2336"},
+		{`select dayname("1962-03-01")+2.333;`, "5.333"},
+		{`select dayname("1962-03-01")>2;`, "1"},
+		{`select dayname("1962-03-01")<2;`, "0"},
+		{`select dayname("1962-03-01")=3;`, "1"},
+		{`select dayname("1962-03-01")!=3;`, "0"},
+		{`select dayname("1962-03-01")<4;`, "1"},
+		{`select dayname("1962-03-01")>4;`, "0"},
+		{`select !dayname("1962-03-01");`, "0"},
+		{`select dayname("1962-03-01")&1;`, "1"},
+		{`select dayname("1962-03-01")&3;`, "3"},
+		{`select dayname("1962-03-01")&7;`, "3"},
+		{`select dayname("1962-03-01")|1;`, "3"},
+		{`select dayname("1962-03-01")|3;`, "3"},
+		{`select dayname("1962-03-01")|7;`, "7"},
+		{`select dayname("1962-03-01")^1;`, "2"},
+		{`select dayname("1962-03-01")^3;`, "0"},
+		{`select dayname("1962-03-01")^7;`, "4"},
+	}
+
+	for _, c := range cases {
+		tk.MustQuery(c.sql).Check(testkit.Rows(c.result))
+	}
+}