evalengine: Implement FROM_DAYS

go/mysql/datetime/mydate.go

@@ -81,3 +81,11 @@
 
 	panic("unreachable: yday is too large?")
 }
+
+// DateFromDayNumber converts an absolute day number into a Date.
+// Returns zero date if day number exceeds 3652499 or is less than 366.
+func DateFromDayNumber(daynr int) Date {
+	var d Date
+	d.year, d.month, d.day = mysqlDateFromDayNumber(daynr)
+	return d
+}

go/vt/vtgate/evalengine/compiler_asm.go

@@ -3795,6 +3795,20 @@ func (asm *assembler) Fn_LAST_DAY() {
 	}, "FN LAST_DAY DATETIME(SP-1)")
 }
 
+func (asm *assembler) Fn_FROM_DAYS() {
+	asm.emit(func(env *ExpressionEnv) int {
+		arg := env.vm.stack[env.vm.sp-1].(*evalInt64)
+		d := datetime.DateFromDayNumber(int(arg.i))
+		if d.Year() > 9999 {
+			env.vm.stack[env.vm.sp-1] = nil
+			return 1
+		}
+
+		env.vm.stack[env.vm.sp-1] = env.vm.arena.newEvalDate(d)
+		return 1
+	}, "FN FROM_DAYS INT64(SP-1)")
+}
+
 func (asm *assembler) Fn_QUARTER() {
 	asm.emit(func(env *ExpressionEnv) int {
 		if env.vm.stack[env.vm.sp-1] == nil {

go/vt/vtgate/evalengine/fn_time.go

@@ -111,6 +111,10 @@
 		CallExpr
 	}
 
+	builtinFromDays struct {
+		CallExpr
+	}
+
 	builtinQuarter struct {
 		CallExpr
 	}
@@ -173,6 +177,7 @@
 var _ IR = (*builtinMonth)(nil)
 var _ IR = (*builtinMonthName)(nil)
 var _ IR = (*builtinLastDay)(nil)
+var _ IR = (*builtinFromDays)(nil)
 var _ IR = (*builtinQuarter)(nil)
 var _ IR = (*builtinSecond)(nil)
 var _ IR = (*builtinTime)(nil)
@@ -1249,6 +1254,42 @@
 	return ctype{Type: sqltypes.Date, Flag: arg.Flag | flagNullable}, nil
 }
 
+func (b *builtinFromDays) eval(env *ExpressionEnv) (eval, error) {
+	arg, err := b.arg1(env)
+	if arg == nil {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	d := datetime.DateFromDayNumber(int(evalToInt64(arg).i))
+
+	// mysql returns NULL if year is greater than 9999
+	if d.Year() > 9999 {
+		return nil, nil
+	}
+	return newEvalDate(d, true), nil
+}
+
+func (call *builtinFromDays) compile(c *compiler) (ctype, error) {
+	arg, err := call.Arguments[0].compile(c)
+	if err != nil {
+		return ctype{}, err
+	}
+
+	skip := c.compileNullCheck1(arg)
+	switch arg.Type {
+	case sqltypes.Int64:
+	default:
+		c.asm.Convert_xi(1)
+	}
+
+	c.asm.Fn_FROM_DAYS()
+	c.asm.jumpDestination(skip)
+	return ctype{Type: sqltypes.Date, Flag: arg.Flag | flagNullable}, nil
+}
+
 func (b *builtinQuarter) eval(env *ExpressionEnv) (eval, error) {
 	date, err := b.arg1(env)
 	if err != nil {

go/vt/vtgate/evalengine/testcases/cases.go

@@ -131,6 +131,7 @@ var Cases = []TestCase{
 	{Run: FnMonth},
 	{Run: FnMonthName},
 	{Run: FnLastDay},
+	{Run: FnFromDays},
 	{Run: FnQuarter},
 	{Run: FnSecond},
 	{Run: FnTime},
@@ -1766,6 +1767,28 @@ func FnLastDay(yield Query) {
 	}
 }
 
+func FnFromDays(yield Query) {
+	for _, d := range inputConversions {
+		yield(fmt.Sprintf("FROM_DAYS(%s)", d), nil)
+	}
+
+	days := []string{
+		"0",
+		"1",
+		"366",
+		"365242",
+		"3652424",
+		"3652425",
+		"3652500",
+		"3652499",
+		"730669",
+	}
+
+	for _, d := range days {
+		yield(fmt.Sprintf("FROM_DAYS(%s)", d), nil)
+	}
+}
+
 func FnQuarter(yield Query) {
 	for _, d := range inputConversions {
 		yield(fmt.Sprintf("QUARTER(%s)", d), nil)

go/vt/vtgate/evalengine/translate_builtin.go

@@ -419,6 +419,11 @@
 			return nil, argError(method)
 		}
 		return &builtinLastDay{CallExpr: call}, nil
+	case "from_days":
+		if len(args) != 1 {
+			return nil, argError(method)
+		}
+		return &builtinFromDays{CallExpr: call}, nil
 	case "quarter":
 		if len(args) != 1 {
 			return nil, argError(method)