golang GoLang数据库SQL：从查询中选择未知数量的列。基准测试结果为db_test.go

Posted 2021-05-24

package main

import (
	"database/sql"
	_ "github.com/go-sql-driver/mysql"
	"testing"
)
//$ go test -v -bench=. -benchmem .
//testing: warning: no tests to run
//PASS
//BenchmarkMapStringScan	 300	   4388248 ns/op	  416755 B/op	   20602 allocs/op
//BenchmarkStrStrScan	     300	   3990020 ns/op	  416629 B/op	   20602 allocs/op
//BenchmarkRowMapString	     200	   7937005 ns/op	 1505452 B/op	   36304 allocs/op
func BenchmarkMapStringScan(b *testing.B) {

	db, err := sql.Open("mysql", "magento-1-8:magento-1-8@tcp(:3306)/magento-1-8")
	if err != nil {
		b.Fatal(err)
	}
	defer db.Close()

	b.ResetTimer()

	for i := 0; i < b.N; i++ {
		rows, err := db.Query(TEST_QUERY)
		if err != nil {
			b.Fatal(err)
		}
		defer rows.Close()
		columnNames, err := rows.Columns()
		if err != nil {
			b.Fatal(err)
		}
		rc := NewMapStringScan(columnNames)
		for rows.Next() {
			err := rc.Update(rows)
			if err != nil {
				b.Fatal(err)
			}
			_ = rc.Get()
		}
	}
}
func BenchmarkStrStrScan(b *testing.B) {

	db, err := sql.Open("mysql", "magento-1-8:magento-1-8@tcp(:3306)/magento-1-8")
	if err != nil {
		b.Fatal(err)
	}
	defer db.Close()

	b.ResetTimer()

	for i := 0; i < b.N; i++ {
		rows, err := db.Query(TEST_QUERY)
		if err != nil {
			b.Fatal(err)
		}
		defer rows.Close()
		columnNames, err := rows.Columns()
		if err != nil {
			b.Fatal(err)
		}
		rc := NewStringStringScan(columnNames)
		for rows.Next() {
			err := rc.Update(rows)
			if err != nil {
				b.Fatal(err)
			}
			_ = rc.Get()
		}
	}
}

func BenchmarkRowMapString(b *testing.B) {

	db, err := sql.Open("mysql", "magento-1-8:magento-1-8@tcp(:3306)/magento-1-8")
	if err != nil {
		b.Fatal(err)
	}
	defer db.Close()
	b.ResetTimer()

	for i := 0; i < b.N; i++ {
		rows, err := db.Query(TEST_QUERY)
		if err != nil {
			b.Fatal(err)
		}
		defer rows.Close()
		columnNames, err := rows.Columns()
		if err != nil {
			b.Fatal(err)
		}

		for rows.Next() {
			_, err := rowMapString(columnNames, rows)
			if err != nil {
				b.Fatal(err)
			}
		}
	}
}

package main

import (
	"database/sql"
	"fmt"
	_ "github.com/go-sql-driver/mysql"
	"log"
)

const (
	// 1745 rows
	// columns are: value_id, entity_type_id, attribute_id, store_id, entity_id, value
	TEST_QUERY = `SELECT * FROM catalog_product_entity_varchar`
)

func main() {
	db, err := sql.Open("mysql", "magento-1-8:magento-1-8@tcp(:3306)/magento-1-8")
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	rows, err := db.Query(TEST_QUERY)
	fck(err)
	defer rows.Close()
	columnNames, err := rows.Columns()
	fck(err)
	rc := NewMapStringScan(columnNames)
	for rows.Next() {
		//        cv, err := rowMapString(columnNames, rows)
		//        fck(err)
		err := rc.Update(rows)
		fck(err)
		cv := rc.Get()
		log.Printf("%#v\n\n", cv)
	}
}

/**
  using a map
*/
type mapStringScan struct {
	// cp are the column pointers
	cp []interface{}
	// row contains the final result
	row      map[string]string
	colCount int
	colNames []string
}

func NewMapStringScan(columnNames []string) *mapStringScan {
	lenCN := len(columnNames)
	s := &mapStringScan{
		cp:       make([]interface{}, lenCN),
		row:      make(map[string]string, lenCN),
		colCount: lenCN,
		colNames: columnNames,
	}
	for i := 0; i < lenCN; i++ {
		s.cp[i] = new(sql.RawBytes)
	}
	return s
}

func (s *mapStringScan) Update(rows *sql.Rows) error {
	if err := rows.Scan(s.cp...); err != nil {
		return err
	}

	for i := 0; i < s.colCount; i++ {
		if rb, ok := s.cp[i].(*sql.RawBytes); ok {
			s.row[s.colNames[i]] = string(*rb)
			*rb = nil // reset pointer to discard current value to avoid a bug
		} else {
			return fmt.Errorf("Cannot convert index %d column %s to type *sql.RawBytes", i, s.colNames[i])
		}
	}
	return nil
}

func (s *mapStringScan) Get() map[string]string {
	return s.row
}

/**
  using a string slice
*/
type stringStringScan struct {
	// cp are the column pointers
	cp []interface{}
	// row contains the final result
	row      []string
	colCount int
	colNames []string
}

func NewStringStringScan(columnNames []string) *stringStringScan {
	lenCN := len(columnNames)
	s := &stringStringScan{
		cp:       make([]interface{}, lenCN),
		row:      make([]string, lenCN*2),
		colCount: lenCN,
		colNames: columnNames,
	}
	j := 0
	for i := 0; i < lenCN; i++ {
		s.cp[i] = new(sql.RawBytes)
		s.row[j] = s.colNames[i]
		j = j + 2
	}
	return s
}

func (s *stringStringScan) Update(rows *sql.Rows) error {
	if err := rows.Scan(s.cp...); err != nil {
		return err
	}
	j := 0
	for i := 0; i < s.colCount; i++ {
		if rb, ok := s.cp[i].(*sql.RawBytes); ok {
			s.row[j+1] = string(*rb)
			*rb = nil // reset pointer to discard current value to avoid a bug
		} else {
			return fmt.Errorf("Cannot convert index %d column %s to type *sql.RawBytes", i, s.colNames[i])
		}
		j = j + 2
	}
	return nil
}

func (s *stringStringScan) Get() []string {
	return s.row
}

// rowMapString was the first implementation but it creates for each row a new
// map and pointers and is considered as slow. see benchmark
func rowMapString(columnNames []string, rows *sql.Rows) (map[string]string, error) {
	lenCN := len(columnNames)
	ret := make(map[string]string, lenCN)

	columnPointers := make([]interface{}, lenCN)
	for i := 0; i < lenCN; i++ {
		columnPointers[i] = new(sql.RawBytes)
	}

	if err := rows.Scan(columnPointers...); err != nil {
		return nil, err
	}

	for i := 0; i < lenCN; i++ {
		if rb, ok := columnPointers[i].(*sql.RawBytes); ok {
			ret[columnNames[i]] = string(*rb)
		} else {
			return nil, fmt.Errorf("Cannot convert index %d column %s to type *sql.RawBytes", i, columnNames[i])
		}
	}

	return ret, nil
}

func fck(err error) {
	if err != nil {
		log.Fatal(err)
	}
}

Golang从数据库中查询数据

执行返回数据的 SQL 语句时，使用包Query 中提供的方法之一database/sql。这些中的每一个都返回一个Row 或其Rows数据，您可以使用该Scan方法将其复制到变量。例如，您将使用这些方法来执行SELECT语句。

执行不返回数据的语句时，可以改用Execor ExecContext方法。有关更多信息，请参阅 执行不返回数据的语句。

该database/sql包提供了两种执行结果查询的方法。

• 查询单行—— 从数据库中QueryRow最多返回一个。

• 查询多行——Query将所有匹配的行作为 Rows代码可以循环的结构返回。

如果您的代码将重复执行相同的 SQL 语句，请考虑使用准备好的语句。