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modify limit offset implement (#2188) 

Oracle and SQLServer specific: When `LIMIT OFFSET` function is needed, use `OFFSET <offset> ROWS FETCH NEXT <limit> ROWS ONLY` to replace legacy subquery.

SQLServer specific: When `ORDER BY` is not set and `OFFSET FETCH` is set, set `statement.orderStr` to `1` (`ORDER BY 1`). See [here](https://learn.microsoft.com/zh-cn/sql/t-sql/queries/select-order-by-clause-transact-sql?view=sql-server-ver16).

MySQL specific: When limit is 0 and offset > 0, use `LIMIT 9223372036854775807` ($2^{63}-1$). See comments [here](15d171ea55/internal/statements/query.go (L314)).

Reviewed-on: https://gitea.com/xorm/xorm/pulls/2188
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: FlyingOnion <731677080@qq.com>
Co-committed-by: FlyingOnion <731677080@qq.com>
This commit is contained in:
FlyingOnion 2023-09-20 02:07:03 +00:00 committed by Lunny Xiao
parent ac88a5705a
commit 551de3767c
6 changed files with 149 additions and 55 deletions
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10
dialects/mssql.go
View File

@ -217,6 +217,7 @@ type mssql struct {
Base
defaultVarchar string
defaultChar string
useLegacy bool
}
func (db *mssql) Init(uri *URI) error {
@ -226,6 +227,8 @@ func (db *mssql) Init(uri *URI) error {
return db.Base.Init(db, uri)
}
func (db *mssql) UseLegacyLimitOffset() bool { return db.useLegacy }
func (db *mssql) SetParams(params map[string]string) {
defaultVarchar, ok := params["DEFAULT_VARCHAR"]
if ok {
@ -252,6 +255,13 @@ func (db *mssql) SetParams(params map[string]string) {
} else {
db.defaultChar = "CHAR"
}
useLegacy, ok := params["USE_LEGACY_LIMIT_OFFSET"]
if ok {
if b, _ := strconv.ParseBool(useLegacy); b {
db.useLegacy = true
}
}
}
func (db *mssql) Version(ctx context.Context, queryer core.Queryer) (*schemas.Version, error) {

12
dialects/oracle.go
View File

@ -509,6 +509,7 @@ var (
type oracle struct {
Base
useLegacy bool
}
func (db *oracle) Init(uri *URI) error {
@ -516,6 +517,17 @@ func (db *oracle) Init(uri *URI) error {
return db.Base.Init(db, uri)
}
func (db *oracle) UseLegacyLimitOffset() bool { return db.useLegacy }
func (db *oracle) SetParams(params map[string]string) {
useLegacy, ok := params["USE_LEGACY_LIMIT_OFFSET"]
if ok {
if b, _ := strconv.ParseBool(useLegacy); b {
db.useLegacy = true
}
}
}
func (db *oracle) Version(ctx context.Context, queryer core.Queryer) (*schemas.Version, error) {
rows, err := queryer.QueryContext(ctx, "select * from v$version where banner like 'Oracle%'")
if err != nil {

59
internal/statements/legacy_select.go Normal file
View File

@ -0,0 +1,59 @@
// Copyright 2022 The Xorm Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package statements
import (
"fmt"
"xorm.io/builder"
)
// isUsingLegacy returns true if xorm uses legacy LIMIT OFFSET.
// It's only available in sqlserver and oracle, if param USE_LEGACY_LIMIT_OFFSET is set to "true"
func (statement *Statement) isUsingLegacyLimitOffset() bool {
u, ok := statement.dialect.(interface{ UseLegacyLimitOffset() bool })
return ok && u.UseLegacyLimitOffset()
}
func (statement *Statement) writeSelectWithFns(buf *builder.BytesWriter, writeFuncs ...func(*builder.BytesWriter) error) (err error) {
for _, fn := range writeFuncs {
if err = fn(buf); err != nil {
return
}
}
return
}
// write mssql legacy query sql
func (statement *Statement) writeMssqlLegacySelect(buf *builder.BytesWriter, columnStr string) error {
writeFns := []func(*builder.BytesWriter) error{
func(bw *builder.BytesWriter) (err error) {
_, err = fmt.Fprintf(bw, "SELECT")
return
},
func(bw *builder.BytesWriter) error { return statement.writeDistinct(bw) },
func(bw *builder.BytesWriter) error { return statement.writeTop(bw) },
statement.writeFrom,
statement.writeWhereWithMssqlPagination,
func(bw *builder.BytesWriter) error { return statement.writeGroupBy(bw) },
func(bw *builder.BytesWriter) error { return statement.writeHaving(bw) },
func(bw *builder.BytesWriter) error { return statement.writeOrderBys(bw) },
func(bw *builder.BytesWriter) error { return statement.writeForUpdate(bw) },
}
return statement.writeSelectWithFns(buf, writeFns...)
}
func (statement *Statement) writeOracleLegacySelect(buf *builder.BytesWriter, columnStr string) error {
writeFns := []func(*builder.BytesWriter) error{
func(bw *builder.BytesWriter) error { return statement.writeSelectColumns(bw, columnStr) },
statement.writeFrom,
func(bw *builder.BytesWriter) error { return statement.writeOracleLimit(bw, columnStr) },
func(bw *builder.BytesWriter) error { return statement.writeGroupBy(bw) },
func(bw *builder.BytesWriter) error { return statement.writeHaving(bw) },
func(bw *builder.BytesWriter) error { return statement.writeOrderBys(bw) },
func(bw *builder.BytesWriter) error { return statement.writeForUpdate(bw) },
}
return statement.writeSelectWithFns(buf, writeFns...)
}

103
internal/statements/query.go
View File

@ -35,7 +35,7 @@ func (statement *Statement) GenQuerySQL(sqlOrArgs ...interface{}) (string, []int
}
buf := builder.NewWriter()
if err := statement.writeSelect(buf, statement.genSelectColumnStr(), true, true); err != nil {
if err := statement.writeSelect(buf, statement.genSelectColumnStr(), true); err != nil {
return "", nil, err
}
return buf.String(), buf.Args(), nil
@ -66,7 +66,7 @@ func (statement *Statement) GenSumSQL(bean interface{}, columns ...string) (stri
}
buf := builder.NewWriter()
if err := statement.writeSelect(buf, strings.Join(sumStrs, ", "), true, true); err != nil {
if err := statement.writeSelect(buf, strings.Join(sumStrs, ", "), true); err != nil {
return "", nil, err
}
return buf.String(), buf.Args(), nil
@ -122,7 +122,7 @@ func (statement *Statement) GenGetSQL(bean interface{}) (string, []interface{},
}
buf := builder.NewWriter()
if err := statement.writeSelect(buf, columnStr, true, true); err != nil {
if err := statement.writeSelect(buf, columnStr, true); err != nil {
return "", nil, err
}
return buf.String(), buf.Args(), nil
@ -168,7 +168,7 @@ func (statement *Statement) GenCountSQL(beans ...interface{}) (string, []interfa
subQuerySelect = selectSQL
}
if err := statement.writeSelect(buf, subQuerySelect, false, false); err != nil {
if err := statement.writeSelect(buf, subQuerySelect, false); err != nil {
return "", nil, err
}
@ -200,7 +200,7 @@ func (statement *Statement) writeLimitOffset(w builder.Writer) error {
_, err := fmt.Fprintf(w, " LIMIT %v OFFSET %v", *statement.LimitN, statement.Start)
return err
}
_, err := fmt.Fprintf(w, " LIMIT 0 OFFSET %v", statement.Start)
_, err := fmt.Fprintf(w, " OFFSET %v", statement.Start)
return err
}
if statement.LimitN != nil {
@ -211,10 +211,20 @@ func (statement *Statement) writeLimitOffset(w builder.Writer) error {
return nil
}
func (statement *Statement) writeTop(w builder.Writer) error {
if statement.dialect.URI().DBType != schemas.MSSQL {
func (statement *Statement) writeOffsetFetch(w builder.Writer) error {
if statement.LimitN != nil {
_, err := fmt.Fprintf(w, " OFFSET %v ROWS FETCH NEXT %v ROWS ONLY", statement.Start, *statement.LimitN)
return err
}
if statement.Start > 0 {
_, err := fmt.Fprintf(w, " OFFSET %v ROWS", statement.Start)
return err
}
return nil
}
// write "TOP <n>" (mssql only)
func (statement *Statement) writeTop(w builder.Writer) error {
if statement.LimitN == nil {
return nil
}
@ -237,9 +247,6 @@ func (statement *Statement) writeSelectColumns(w *builder.BytesWriter, columnStr
if err := statement.writeDistinct(w); err != nil {
return err
}
if err := statement.writeTop(w); err != nil {
return err
}
_, err := fmt.Fprint(w, " ", columnStr)
return err
}
@ -284,8 +291,10 @@ func (statement *Statement) writeForUpdate(w io.Writer) error {
return err
}
// write subquery to implement limit offset
// (mssql legacy only)
func (statement *Statement) writeMssqlPaginationCond(w *builder.BytesWriter) error {
if statement.dialect.URI().DBType != schemas.MSSQL || statement.Start <= 0 {
if statement.Start <= 0 {
return nil
}
@ -365,41 +374,55 @@ func (statement *Statement) writeOracleLimit(w *builder.BytesWriter, columnStr s
return err
}
func (statement *Statement) writeSelect(buf *builder.BytesWriter, columnStr string, needLimit, needOrderBy bool) error {
if err := statement.writeSelectColumns(buf, columnStr); err != nil {
return err
func (statement *Statement) writeSelect(buf *builder.BytesWriter, columnStr string, needLimit bool) error {
dbType := statement.dialect.URI().DBType
if statement.isUsingLegacyLimitOffset() {
if dbType == "mssql" {
return statement.writeMssqlLegacySelect(buf, columnStr)
}
if err := statement.writeFrom(buf); err != nil {
return err
}
if err := statement.writeWhereWithMssqlPagination(buf); err != nil {
return err
}
if err := statement.writeGroupBy(buf); err != nil {
return err
}
if err := statement.writeHaving(buf); err != nil {
return err
}
if needOrderBy {
if err := statement.writeOrderBys(buf); err != nil {
return err
if dbType == "oracle" {
return statement.writeOracleLegacySelect(buf, columnStr)
}
}
dialect := statement.dialect
if needLimit {
if dialect.URI().DBType == schemas.ORACLE {
if err := statement.writeOracleLimit(buf, columnStr); err != nil {
return err
// TODO: modify all functions to func(w builder.Writer) error
writeFns := []func(*builder.BytesWriter) error{
func(bw *builder.BytesWriter) error { return statement.writeSelectColumns(bw, columnStr) },
statement.writeFrom,
statement.writeWhere,
func(bw *builder.BytesWriter) error { return statement.writeGroupBy(bw) },
func(bw *builder.BytesWriter) error { return statement.writeHaving(bw) },
func(bw *builder.BytesWriter) (err error) {
if dbType == "mssql" && len(statement.orderBy) == 0 && needLimit {
// ORDER BY is mandatory to use OFFSET and FETCH clause (only in sqlserver)
if statement.LimitN == nil && statement.Start == 0 {
// no need to add
return
}
} else if dialect.URI().DBType != schemas.MSSQL {
if err := statement.writeLimitOffset(buf); err != nil {
return err
if statement.IsDistinct || len(statement.GroupByStr) > 0 {
// the order-by column should be one of distincts or group-bys
// order by the first column
_, err = bw.WriteString(" ORDER BY 1 ASC")
return
}
if statement.RefTable == nil || len(statement.RefTable.PrimaryKeys) != 1 {
// no primary key, order by the first column
_, err = bw.WriteString(" ORDER BY 1 ASC")
return
}
// order by primary key
statement.orderBy = []orderBy{{orderStr: statement.colName(statement.RefTable.GetColumn(statement.RefTable.PrimaryKeys[0]), statement.TableName()), direction: "ASC"}}
}
return statement.writeForUpdate(buf)
return statement.writeOrderBys(bw)
},
func(bw *builder.BytesWriter) error {
if dbType == "mssql" || dbType == "oracle" {
return statement.writeOffsetFetch(bw)
}
return statement.writeLimitOffset(bw)
},
func(bw *builder.BytesWriter) error { return statement.writeForUpdate(bw) },
}
return statement.writeSelectWithFns(buf, writeFns...)
}
// GenExistSQL generates Exist SQL
@ -522,7 +545,7 @@ func (statement *Statement) GenFindSQL(autoCond builder.Cond) (string, []interfa
statement.cond = statement.cond.And(autoCond)
buf := builder.NewWriter()
if err := statement.writeSelect(buf, statement.genSelectColumnStr(), true, true); err != nil {
if err := statement.writeSelect(buf, statement.genSelectColumnStr(), true); err != nil {
return "", nil, err
}
return buf.String(), buf.Args(), nil

9
tests/session_count_test.go
View File

@ -118,16 +118,11 @@ func TestWithTableName(t *testing.T) {
})
assert.NoError(t, err)
total, err := testEngine.OrderBy("count(`id`) desc").Count(new(CountWithTableName))
total, err := testEngine.Count(new(CountWithTableName))
assert.NoError(t, err)
assert.EqualValues(t, 2, total)
total, err = testEngine.OrderBy("count(`id`) desc").Count(CountWithTableName{})
assert.NoError(t, err)
assert.EqualValues(t, 2, total)
// the orderby will be ignored by count because some databases will return errors if the orderby columns not in group by
total, err = testEngine.OrderBy("`name`").Count(CountWithTableName{})
total, err = testEngine.Count(CountWithTableName{})
assert.NoError(t, err)
assert.EqualValues(t, 2, total)
}

5
tests/session_query_test.go
View File

@ -365,11 +365,6 @@ func TestJoinWithSubQuery(t *testing.T) {
func TestQueryStringWithLimit(t *testing.T) {
assert.NoError(t, PrepareEngine())
if testEngine.Dialect().URI().DBType == schemas.MSSQL {
t.SkipNow()
return
}
type QueryWithLimit struct {
Id int64 `xorm:"autoincr pk"`
Msg string `xorm:"varchar(255)"`