Go Mysql驱动

Golang中MYSQL驱动

• Mysql库https://github.com/go-sql-driver/mysql
• Go本身不提供具体数据库驱动，只提供驱动接口和管理。
• 各个数据库驱动需要第三方实现，并且注册到Go中的驱动管理中。

安装golang mysql drvier

go get github.com/go-sql-driver/mysql

代码中需要注册mysql数据库驱动，通过引入空白导入mysql包来完成。

为什么需要使用空白导入？ 是因为需要执行mysql包的初始化代码（代码位于%GOPATH%/github.com/go-sql-driver/mysql/driver.go）

func init() {
    sql.Register("mysql", &MySQLDriver{})
}

连接数据的DSN格式

username:password@protocol(address)/dbname?param=value

Prepared Statement 
sql.Stmt支持预备表达式，可以用来优化SQL查询提高性能，减少SQL注入的风险, DB.Prepare()和Tx.Prepare()都提供了对于预备表达式的支持。

预处理的流程:
step1. 将sql分为2部分.命令部分和数据部分.
step2. 首先将命令部分发送给mysql服务器,mysql进行预处理.(如生成AST)
step3. 然后将数据部分发送给mysql服务器,mysql进行占位符替换.
step4. mysql服务器执行sql语句,把执行结果发送给客户端.

预处理的优势:
1.因为发送命令后,在mysql服务器端,就会将AST生成好,所以不需要对每一次值的更换都重新生成一次AST.对同样的数据不同的SQL来讲,只需生成1次AST,并缓存起来即可.
2.避免SQL注入.因为mysql知道再次发送过来的内容为”数据”,因此不会将这些数据解析为SQL,避免了SQL注入.

需要注意的点:
使用预处理进行查询操作时,不仅在defer时需要关闭结果集,而且还要关闭命令句柄,否则同样会占用连接,导致阻塞.

package main

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

type User struct {
Id int `db:"id"`
Name string `db:"name"`
Age int `db:"age"`
}

func PrepareQuery(db *sql.DB, id int) {
stmt, err := db.Prepare("select id, name, age from user where id>?")
if err != nil {
panic(err)
}

rows, err := stmt.Query(id)
if err != nil {
panic(err)
}

defer stmt.Close()
defer rows.Close()

for rows.Next(){
var user User
err := rows.Scan(&user.Id, &user.Name, &user.Age)
if err != nil {
panic(err)
}
fmt.Printf("user: %#v ", user)
}
}

func main() {

dns := "root:123456@tcp(172.16.65.200:3306)/golang"
db, err := sql.Open("mysql", dns)
if err != nil {
panic(err)
}

defer db.Close()

PrepareQuery(db, 0)

}

Mysql创建表：

　　CREATE TABLE user (

　　id int(20) NOT NULL AUTO_INCREMENT,

　　name varchar(20) DEFAULT '',

　　age int(2) DEFAULT '0',

　　PRIMARY KEY (id))

　　ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT  CHARSET=utf8mb4;

数据库增删改查

insert

package main

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

func Insert(db *sql.DB) {
name := "Vincent"
age := 18

result, err := db.Exec("insert into user(name, age) values (?,?)", name, age)
if err != nil {
panic(err)
}

id, err := result.LastInsertId()
if err != nil {
panic(err)
}

affected, err := result.RowsAffected()
if err != nil {
panic(err)
}

fmt.Printf("last insert id:%d affect rows:%d ", id, affected)
}

func main() {
dns := "root:123456@tcp(172.16.65.200:3306)/golang"
db, err := sql.Open("mysql", dns)
if err != nil {
panic(err)
}

err = db.Ping()
if err != nil {
panic(err)
}
fmt.Println("connect to db success!!!")
Insert(db)
}

package main

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

func Insert(db *sql.DB) {
    name := "Vincent"
    age := 18

    result, err := db.Exec("insert into user(name, age) values (?,?)", name, age)
    if err != nil {
        panic(err)
    }

    id, err := result.LastInsertId()
    if err != nil {
        panic(err)
    }

    affected, err := result.RowsAffected()
    if err != nil {
        panic(err)
    }

    fmt.Printf("last insert id:%d affect rows:%d
", id, affected)
}

func main() {
    dns := "root:123456@tcp(172.16.65.200:3306)/golang"
    db, err := sql.Open("mysql", dns)
    if err != nil {
        panic(err)
    }

    err = db.Ping()
    if err != nil {
        panic(err)
    }
    fmt.Println("connect to db success!!!")
    Insert(db)
}

delete

package main

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

func Delete(db *sql.DB, id int) {
result, err := db.Exec("delete from user where id=?", id)
if err != nil {
panic(err)
}

rowsAffected, err := result.RowsAffected()
if err != nil {
panic(err)
}
fmt.Printf("delect id:%d, affect rows:%d ", id, rowsAffected)
}

func main() {
dns := "root:123456@tcp(172.16.65.200:3306)/golang"
db, _ := sql.Open("mysql", dns)
Delete(db, 2)
}

package main

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

func Delete(db *sql.DB, id int) {
    result, err := db.Exec("delete from user where id=?", id)
    if err != nil {
        panic(err)
    }

    rowsAffected, err := result.RowsAffected()
    if err != nil {
        panic(err)
    }
    fmt.Printf("delect id:%d, affect rows:%d
", id, rowsAffected)
}

func main() {
    dns := "root:123456@tcp(172.16.65.200:3306)/golang"
    db, _ := sql.Open("mysql", dns)
    Delete(db, 2)
}

update

package main

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

func Update(db *sql.DB) {
name := "Miles"
age := 88
id := 3

result, err := db.Exec("update user set name=?, age=? where id=?", name, age, id)
if err != nil {
panic(err)
}

// RowsAffected returns the number of rows affected by an
// update, insert, or delete.
rowsAffected, err := result.RowsAffected()
if err != nil {
panic(err)
}

fmt.Printf("update id:%d, affect rows:%d ", id, rowsAffected)

}

func main() {
dns := "root:123456@tcp(172.16.65.200:3306)/golang"
db, err := sql.Open("mysql", dns)
if err != nil {
panic(err)
}

err = db.Ping()
if err != nil {
panic(err)
}
fmt.Println("connect to db success!!!")
Update(db)
}

package main

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

func Update(db *sql.DB) {
    name := "Miles"
    age := 88
    id := 3

    result, err := db.Exec("update user set name=?, age=? where id=?", name, age, id)
    if err != nil {
        panic(err)
    }

    // RowsAffected returns the number of rows affected by an
    // update, insert, or delete.
    rowsAffected, err := result.RowsAffected()
    if err != nil {
        panic(err)
    }

    fmt.Printf("update id:%d, affect rows:%d
", id, rowsAffected)

}

func main() {
    dns := "root:123456@tcp(172.16.65.200:3306)/golang"
    db, err := sql.Open("mysql", dns)
    if err != nil {
        panic(err)
    }

    err = db.Ping()
    if err != nil {
        panic(err)
    }
    fmt.Println("connect to db success!!!")
    Update(db)
}

query

package main

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

type User struct {
Id int `db:"id"`
Name string `db:"name"`
Age int `db:"age"`
}

// 单行查询，如果查询到多个结果，只返回第一行，查询不到结果就ErrNoRows错误。
func QueryRow(db *sql.DB) {
id:= 2
row := db.QueryRow("select id, name, age from user where id=?", id)

var user User
err := row.Scan(&user.Id, &user.Name, &user.Age)

if err == sql.ErrNoRows {
log.Printf("not found data of the id:%d",id)
}

if err != nil {
panic(err)
}

fmt.Printf("user: %#v ", user)
}

// 多行查询, 查询不到任何记录也不会报错。
func Query(db *sql.DB) {
id := 0
rows, err := db.Query("select id, name, age from user where id>?", id)
if err != nil {
panic(err)
}
if err == sql.ErrNoRows {
log.Printf("not found data of id:%d ", id)
return
}
defer rows.Close()

for rows.Next() {
var user User
err := rows.Scan(&user.Id, &user.Name, &user.Age)
if err != nil {
panic(err)
}
fmt.Printf("user: %#v ", user)
}

}

func main() {
dns := "root:123456@tcp(172.16.65.200:3306)/golang"
db, err := sql.Open("mysql", dns)
if err != nil {
panic(err)
}

err = db.Ping()
if err != nil {
panic(err)
}

fmt.Printf("connect to db success ")

//QueryRow(db)

Query(db)
}

package main

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

type User struct {
    Id int `db:"id"`
    Name string `db:"name"`
    Age int `db:"age"`
}



// 单行查询，如果查询到多个结果，只返回第一行，查询不到结果就ErrNoRows错误。
func QueryRow(db *sql.DB) {
    id:= 2
    row := db.QueryRow("select id, name, age from user where id=?", id)

    var user User
    err := row.Scan(&user.Id, &user.Name, &user.Age)

    if err == sql.ErrNoRows {
        log.Printf("not found data of the id:%d",id)
    }

    if err != nil {
        panic(err)
    }


    fmt.Printf("user: %#v
", user)
}


// 多行查询, 查询不到任何记录也不会报错。
func Query(db *sql.DB) {
    id := 0
    rows, err := db.Query("select id, name, age from user where id>?", id)
    if err != nil {
        panic(err)
    }
    if err == sql.ErrNoRows {
        log.Printf("not found data of id:%d
", id)
        return
    }
    defer rows.Close()

    for rows.Next() {
        var user User
        err := rows.Scan(&user.Id, &user.Name, &user.Age)
        if err != nil {
            panic(err)
        }
        fmt.Printf("user: %#v
", user)
    }

}

func main() {
    dns := "root:123456@tcp(172.16.65.200:3306)/golang"
    db, err := sql.Open("mysql", dns)
    if err != nil {
        panic(err)
    }

    err = db.Ping()
    if err != nil {
        panic(err)
    }

    fmt.Printf("connect to db success
")

    //QueryRow(db)

    Query(db)
}

事务支持 

事务(transaction)

• transaction, err := Db.Begin() 开启事务
• transaction.Exec() 执行事务
• transaction.Commit() 提交事务
• transaction.Rollback() 回滚事务

A. 事务的应用场景
　　1. 同时更新多个表
　　2. 同时更新多行数据
B. 事务的ACID
　　1. 原子性
　　2. 一致性
　　3. 隔离性
　　4. 持久性

需要注意的点:
1. 执行失败要回滚
2. 提交失败要回滚

package main

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

func Transaction(db *sql.DB) {

// 开启事务
tx, err := db.Begin()

if err != nil {
panic(err)
}

result, err := tx.Exec("insert into user(name, age)values(?,?)", "Jack", 98)
if err != nil {
// 失败回滚
tx.Rollback()
panic(err)
}

fmt.Println("result", result)

exec, err := tx.Exec("update user set name=?, age=? where id=?", "Jack", 98, 1)
if err != nil {
// 失败回滚
tx.Rollback()
panic(err)
}
fmt.Println("exec", exec)

// 提交事务
err = tx.Commit()

if err != nil {
// 失败回滚
tx.Rollback()
panic(err)
}
}

func main() {

dns := "root:123456@tcp(172.16.65.200:3306)/golang"
db, err := sql.Open("mysql", dns)
if err != nil {
panic(err)
}

err = db.Ping()
if err != nil {
panic(err)
}

Transaction(db)
}

package main

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


func Transaction(db *sql.DB) {

    // 开启事务
    tx, err := db.Begin()

    if err != nil {
        panic(err)
    }

    result, err := tx.Exec("insert into user(name, age)values(?,?)", "Jack", 98)
    if err != nil {
        // 失败回滚
        tx.Rollback()
        panic(err)
    }
    
    fmt.Println("result", result)

    exec, err := tx.Exec("update user set name=?, age=? where id=?", "Jack", 98, 1)
    if err != nil {
        // 失败回滚
        tx.Rollback()
        panic(err)
    }
    fmt.Println("exec", exec)

    // 提交事务
    err = tx.Commit()
    
    if err != nil {
        // 失败回滚
        tx.Rollback()
        panic(err)
    }
}

func main() {

    dns := "root:123456@tcp(172.16.65.200:3306)/golang"
    db, err := sql.Open("mysql", dns)
    if err != nil {
        panic(err)
    }

    err = db.Ping()
    if err != nil {
        panic(err)
    }

    Transaction(db)
}

Mysql日期时间类型报错

sql: Scan error on column index 1: unsupported Scan, storing driver.Value type []uint8 into type *time.Time

原因是在调用sql.Open()时没有将parseTime设置为True。加入parseTime即可修复问题：

db, err := sql.Open("mysql", "user:password@tcp(127.0.0.1:3306)/dbname?parseTime=true")