support to_days() and from_days()

enginetest/queries/queries.go

@@ -9591,6 +9591,19 @@ from typestable`,
 			{3},
 		},
 	},
+
+	{
+		Query: "select to_days('2024-04-15');",
+		Expected: []sql.Row{
+			{739356},
+		},
+	},
+	{
+		Query: "select from_days(739356);",
+		Expected: []sql.Row{
+			{time.Date(2024, 4, 15, 0, 0, 0, 0, time.UTC)},
+		},
+	},
 }
 
 var KeylessQueries = []QueryTest{

sql/expression/function/date_test.go

@@ -81,6 +81,18 @@ func TestAddDate(t *testing.T) {
 	result, err = f.Eval(ctx, sql.Row{"asdasdasd"})
 	require.NoError(err)
 	require.Nil(result)
+
+	// If the second argument is NOT an interval, then it's assumed to be a day interval
+	t.Skip("Interval does not handle overflows correctly")
+	f, err = NewAddDate(
+		expression.NewLiteral("2018-05-02", types.Text),
+		expression.NewLiteral(int64(1_000_000), types.Int64))
+	require.NoError(err)
+	expected = time.Date(4756, time.March, 29, 0, 0, 0, 0, time.UTC)
+	result, err = f.Eval(ctx, sql.Row{})
+	require.NoError(err)
+	require.Equal(expected, result)
+
 }
 
 func TestDateAdd(t *testing.T) {

sql/expression/function/days.go

@@ -0,0 +1,234 @@
+// Copyright 2024 Dolthub, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package function
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/dolthub/go-mysql-server/sql"
+	"github.com/dolthub/go-mysql-server/sql/expression"
+	"github.com/dolthub/go-mysql-server/sql/types"
+)
+
+// ToDays is a function that converts a date to a number of days since year 0.
+type ToDays struct {
+	expression.UnaryExpression
+}
+
+var _ sql.FunctionExpression = (*ToDays)(nil)
+var _ sql.CollationCoercible = (*ToDays)(nil)
+
+// NewToDays creates a new ToDays function.
+func NewToDays(date sql.Expression) sql.Expression {
+	return &ToDays{expression.UnaryExpression{Child: date}}
+}
+
+// CollationCoercibility implements sql.CollationCoercible
+func (t *ToDays) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
+	return sql.Collation_binary, 5
+}
+
+// String implements sql.Stringer
+func (t *ToDays) String() string {
+	return fmt.Sprintf("%s(%s)", t.FunctionName(), t.Child.String())
+}
+
+// FunctionName implements sql.FunctionExpression
+func (t *ToDays) FunctionName() string {
+	return "to_days"
+}
+
+// Description implements sql.FunctionExpression
+func (t *ToDays) Description() string {
+	return "return the date argument converted to days"
+}
+
+// Type implements sql.Expression
+func (t *ToDays) Type() sql.Type {
+	return types.Int64
+}
+
+// WithChildren implements sql.Expression
+func (t *ToDays) WithChildren(children ...sql.Expression) (sql.Expression, error) {
+	if len(children) != 1 {
+		return nil, sql.ErrInvalidChildrenNumber.New(t, len(children), 1)
+	}
+	return NewToDays(children[0]), nil
+}
+
+// countLeapYears returns the number of leap years between year 0 and the given year
+func countLeapYears(year int) int {
+	if year < 0 {
+		return 0
+	}
+	return year/4 - year/100 + year/400
+}
+
+// Eval implements sql.Expression
+func (t *ToDays) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
+	date, err := t.Child.Eval(ctx, row)
+	if err != nil {
+		return nil, err
+	}
+	if date == nil {
+		return nil, nil
+	}
+
+	// Special case for zero date
+	if dateStr, isStr := date.(string); isStr && (dateStr == types.ZeroDateStr || dateStr == types.ZeroTimestampDatetimeStr) {
+		return nil, nil
+	}
+
+	date, _, err = types.Date.Convert(date)
+	if err != nil {
+		ctx.Warn(1292, err.Error())
+		return nil, nil
+	}
+	d := date.(time.Time)
+
+	// Using zeroTime.Sub(date) doesn't work because it overflows time.Duration
+	// so we need to calculate the number of days manually
+	// Additionally, MySQL states that this function isn't really accurate for dates before the year 1582
+	years := d.Year()
+
+	// YearDay includes leap day, so we subtract 1 from years to not count it twice
+	res := 365*years + countLeapYears(years-1) + d.YearDay()
+	return res, nil
+}
+
+// FromDays is a function that returns date for a given number of days since year 0.
+type FromDays struct {
+	expression.UnaryExpression
+}
+
+var _ sql.FunctionExpression = (*FromDays)(nil)
+var _ sql.CollationCoercible = (*FromDays)(nil)
+
+// NewFromDays creates a new FromDays function.
+func NewFromDays(days sql.Expression) sql.Expression {
+	return &FromDays{expression.UnaryExpression{Child: days}}
+}
+
+// CollationCoercibility implements sql.CollationCoercible
+func (f *FromDays) CollationCoercibility(ctx *sql.Context) (collation sql.CollationID, coercibility byte) {
+	return sql.Collation_binary, 5
+}
+
+// String implements sql.Stringer
+func (f *FromDays) String() string {
+	return fmt.Sprintf("%s(%s)", f.FunctionName(), f.Child.String())
+}
+
+// FunctionName implements sql.FunctionExpression
+func (f *FromDays) FunctionName() string {
+	return "from_days"
+}
+
+// Description implements sql.FunctionExpression
+func (f *FromDays) Description() string {
+	return "convert a day number to a date"
+}
+
+// Type implements sql.Expression
+func (f *FromDays) Type() sql.Type {
+	return types.Date
+}
+
+// WithChildren implements sql.Expression
+func (f *FromDays) WithChildren(children ...sql.Expression) (sql.Expression, error) {
+	if len(children) != 1 {
+		return nil, sql.ErrInvalidChildrenNumber.New(f, len(children), 1)
+	}
+	return NewFromDays(children[0]), nil
+}
+
+const (
+	DaysPerYear     = 365
+	DaysPer400Years = 400*DaysPerYear + 97
+	DaysPer100Years = 100*DaysPerYear + 24
+	DaysPer4Years   = 4*DaysPerYear + 1
+)
+
+// daysToYear converts a number of days to number of years since year 0 (including leap years), and the remaining days
+func daysToYear(days int64) (int64, int64) {
+	// Special case for year 0, which is not a leap year
+	years := int64(1)
+	days -= DaysPerYear
+
+	years += 400 * (days / DaysPer400Years)
+	days %= DaysPer400Years
+
+	years += 100 * (days / DaysPer100Years)
+	days %= DaysPer100Years
+
+	years += 4 * (days / DaysPer4Years)
+	days %= DaysPer4Years
+
+	years += days / DaysPerYear
+	days %= DaysPerYear
+
+	return years, days
+}
+
+func isLeapYear(year int64) bool {
+	return year != 0 && ((year%4 == 0 && year%100 != 0) || year%400 == 0)
+}
+
+var daysPerMonth = [12]int64{31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
+
+// daysToMonth converts a number of days to the month and the remaining days in that month
+func daysToMonth(year, days int64) (int64, int64) {
+	for i, m := range daysPerMonth {
+		if i == 1 && isLeapYear(year) {
+			m++ // leap day
+		}
+		if days < m {
+			return int64(i + 1), days
+		}
+		days -= m
+	}
+	return -1, -1 // should be impossible
+}
+
+// Eval implements sql.Expression
+func (f *FromDays) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
+	d, err := f.Child.Eval(ctx, row)
+	if err != nil {
+		return nil, err
+	}
+	if d == nil {
+		return nil, nil
+	}
+
+	d, _, err = types.Int64.Convert(d)
+	if err != nil {
+		ctx.Warn(1292, err.Error())
+		return "0000-00-00", nil
+	}
+
+	days, ok := d.(int64)
+	if !ok {
+		return "0000-00-00", nil
+	}
+
+	// For some reason, MySQL returns 0000-00-00 for days <= 365
+	if days <= DaysPerYear {
+		return "0000-00-00", nil
+	}
+	years, days := daysToYear(days)
+	months, days := daysToMonth(years, days)
+	return time.Date(int(years), time.Month(months), int(days), 0, 0, 0, 0, time.UTC), nil
+}