optimize codes & add benchmark test for limit query

Author: BetaCat0

builder_limit.go

@@ -28,9 +28,11 @@ func (b *Builder) limitWriteTo(w Writer) error {
 
 switch strings.ToLower(strings.TrimSpace(b.dialect)) {
 case ORACLE:
-// flush writer, both buffer & args
-ow.writer.Reset()
-ow.args = nil
+if ow.writer.Len() > 0 {
+// flush writer, both buffer & args
+ow.writer.Reset()
+ow.args = nil
+}
 
 selects := b.selects
 b.selects = append(selects, "ROWNUM RN")
@@ -62,9 +64,11 @@ func (b *Builder) limitWriteTo(w Writer) error {
 fmt.Fprintf(ow, " LIMIT %v OFFSET %v", limit.limitN, limit.offset)
 }
 case MSSQL:
-// flush writer, both buffer & args
-ow.writer.Reset()
-ow.args = nil
+if ow.writer.Len() > 0 {
+// flush writer, both buffer & args
+ow.writer.Reset()
+ow.args = nil
+}
 
 selects := b.selects
 if limit.offset == 0 {

builder_select_test.go

@@ -6,6 +6,7 @@ package builder
 
 import (
 "fmt"
+"math/rand"
 "testing"
 
 "github.com/stretchr/testify/assert"
@@ -203,3 +204,116 @@ func TestBuilder_Limit(t *testing.T) {
 assert.EqualValues(t, 3, len(args))
 fmt.Println(sql, args)
 }
+
+func BenchmarkBuilder_Limit(b *testing.B) {
+for i := 0; i < b.N; i++ {
+b.StopTimer()
+builder := randQuery(rand.Intn(1000) >= 500, true)
+b.StartTimer()
+
+_, _, err := builder.ToSQL()
+assert.NoError(b, err)
+}
+}
+
+func TestRandQuery(t *testing.T) {
+sql, args, err := randQuery(false, true).ToSQL()
+assert.NoError(t, err)
+fmt.Println(sql, args)
+
+sql, args, err = randQuery(false, false).ToSQL()
+assert.NoError(t, err)
+fmt.Println(sql, args)
+
+sql, args, err = randQuery(true, false).ToSQL()
+assert.NoError(t, err)
+fmt.Println(sql, args)
+
+sql, args, err = randQuery(true, true).ToSQL()
+assert.NoError(t, err)
+fmt.Println(sql, args)
+}
+
+// randQuery Generate a basic query for benchmark test. But be careful it's not a executable SQL in real db.
+func randQuery(allowUnion, allowLimit bool) *Builder {
+b := randSimpleQuery(allowLimit)
+if allowUnion {
+r := rand.Intn(3) + 1
+for i := r; i < r; i++ {
+b = b.Union("all", randSimpleQuery(allowLimit))
+}
+}
+
+return b
+}
+
+func randSimpleQuery(allowLimit bool) *Builder {
+b := Dialect(randDialect()).Select(randSelects()...).From(randTableName(0)).PK("id")
+b = randJoin(b, 3)
+b = b.Where(randCond(b.selects, 3))
+if allowLimit {
+b = randLimit(b)
+}
+
+return b
+}
+
+func randDialect() string {
+dialects := []string{MYSQL, ORACLE, MSSQL, SQLITE, POSTGRES}
+
+return dialects[rand.Intn(len(dialects))]
+}
+
+func randSelects() []string {
+selects := []string{"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k"}
+
+if rand.Intn(1000) > 900 {
+return []string{"*"}
+}
+
+rdx := rand.Intn(len(selects) / 2)
+return selects[rdx:]
+}
+
+func randTableName(offset int) string {
+return fmt.Sprintf("table%v", rand.Intn(10)+offset)
+}
+
+func randJoin(b *Builder, lessThan int) *Builder {
+if lessThan <= 0 {
+return b
+}
+
+times := rand.Intn(lessThan)
+
+for i := 0; i < times; i++ {
+tableName := randTableName(i * 10)
+b = b.Join("", tableName, fmt.Sprintf("%v.id = %v.id", b.TableName(), tableName))
+}
+
+return b
+}
+
+func randCond(selects []string, lessThan int) Cond {
+if len(selects) <= 0 {
+return nil
+}
+
+cond := NewCond()
+
+times := rand.Intn(lessThan)
+for i := 0; i < times; i++ {
+cond = cond.And(Eq{selects[rand.Intn(len(selects))]: "expected"})
+}
+
+return cond
+}
+
+func randLimit(b *Builder) *Builder {
+r := rand.Intn(1000) + 1
+if r > 500 {
+return b.Limit(r, 1000)
+} else {
+return b.Limit(r)
+}
+}