Merging other languages
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James Miranda
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en/05.4.md
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# 5.4 使用PostgreSQL数据库
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PostgreSQL 是一个自由的对象-关系数据库服务器(数据库管理系统)，它在灵活的 BSD-风格许可证下发行。它提供了相对其他开放源代码数据库系统(比如 MySQL 和 Firebird)，和对专有系统比如 Oracle、Sybase、IBM 的 DB2 和 Microsoft SQL Server的一种选择。
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PostgreSQL和MySQL比较，它更加庞大一点，因为它是用来替代Oracle而设计的。所以在企业应用中采用PostgreSQL是一个明智的选择。
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MySQL被Oracle收购之后正在逐步的封闭（自MySQL 5.5.31以后的所有版本将不再遵循GPL协议），鉴于此，将来我们也许会选择PostgreSQL而不是MySQL作为项目的后端数据库。
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## 驱动
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Go实现的支持PostgreSQL的驱动也很多，因为国外很多人在开发中使用了这个数据库。
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- https://github.com/lib/pq 支持database/sql驱动，纯Go写的
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- https://github.com/jbarham/gopgsqldriver 支持database/sql驱动，纯Go写的
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- https://github.com/lxn/go-pgsql 支持database/sql驱动，纯Go写的
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在下面的示例中我采用了第一个驱动，因为它目前使用的人最多，在github上也比较活跃。
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## 实例代码
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数据库建表语句：
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CREATE TABLE userinfo
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(
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uid serial NOT NULL,
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username character varying(100) NOT NULL,
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departname character varying(500) NOT NULL,
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Created date,
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CONSTRAINT userinfo_pkey PRIMARY KEY (uid)
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)
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WITH (OIDS=FALSE);
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CREATE TABLE userdeatail
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(
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uid integer,
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intro character varying(100),
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profile character varying(100)
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)
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WITH(OIDS=FALSE);
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看下面这个Go如何操作数据库表数据:增删改查
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package main
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import (
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"database/sql"
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"fmt"
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_ "https://github.com/lib/pq"
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)
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func main() {
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db, err := sql.Open("postgres", "user=astaxie password=astaxie dbname=test sslmode=disable")
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checkErr(err)
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//插入数据
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stmt, err := db.Prepare("INSERT INTO userinfo(username,departname,created) VALUES($1,$2,$3) RETURNING uid")
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checkErr(err)
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res, err := stmt.Exec("astaxie", "研发部门", "2012-12-09")
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checkErr(err)
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//pg不支持这个函数，因为他没有类似MySQL的自增ID
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id, err := res.LastInsertId()
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checkErr(err)
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fmt.Println(id)
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//更新数据
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stmt, err = db.Prepare("update userinfo set username=$1 where uid=$2")
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checkErr(err)
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res, err = stmt.Exec("astaxieupdate", 1)
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checkErr(err)
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affect, err := res.RowsAffected()
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checkErr(err)
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fmt.Println(affect)
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//查询数据
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rows, err := db.Query("SELECT * FROM userinfo")
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checkErr(err)
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for rows.Next() {
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var uid int
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var username string
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var department string
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var created string
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err = rows.Scan(&uid, &username, &department, &created)
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checkErr(err)
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fmt.Println(uid)
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fmt.Println(username)
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fmt.Println(department)
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fmt.Println(created)
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}
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//删除数据
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stmt, err = db.Prepare("delete from userinfo where uid=$1")
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checkErr(err)
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res, err = stmt.Exec(1)
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checkErr(err)
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affect, err = res.RowsAffected()
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checkErr(err)
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fmt.Println(affect)
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db.Close()
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}
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func checkErr(err error) {
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if err != nil {
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panic(err)
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}
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}
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从上面的代码我们可以看到，PostgreSQL是通过`$1`,`$2`这种方式来指定要传递的参数，而不是MySQL中的`?`，另外在sql.Open中的dsn信息的格式也与MySQL的驱动中的dsn格式不一样，所以在使用时请注意它们的差异。
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还有pg不支持LastInsertId函数，因为PostgreSQL内部没有实现类似MySQL的自增ID返回，其他的代码几乎是一模一样。
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## links
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* [目录](<preface.md>)
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* 上一节: [使用SQLite数据库](<05.3.md>)
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* 下一节: [使用beedb库进行ORM开发](<05.5.md>)
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# 5.4 PostgreSQL
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PostgreSQL is an object-relational database management system available for many platforms including Linux, FreeBSD, Solaris, Microsoft Windows and Mac OS X. It is released under an MIT-style license, and is thus free and open source software. It's larger than MySQL because it's designed for enterprise usage like Oracle. Postgresql is good choice for enterprise type projects.
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## PostgreSQL drivers
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There are many database drivers available for PostgreSQL. Here are three examples of them:
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- [https://github.com/bmizerany/pq](https://github.com/bmizerany/pq) supports `database/sql`, written in pure Go.
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- [https://github.com/jbarham/gopgsqldriver](https://github.com/jbarham/gopgsqldriver) supports `database/sql`, written in pure Go.
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- [https://github.com/lxn/go-pgsql](https://github.com/lxn/go-pgsql) supports `database/sql`, written in pure Go.
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I'll use the first one in my following examples.
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## Samples
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We create the following SQL:
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CREATE TABLE userinfo
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(
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uid serial NOT NULL,
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username character varying(100) NOT NULL,
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departname character varying(500) NOT NULL,
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Created date,
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CONSTRAINT userinfo_pkey PRIMARY KEY (uid)
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)
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WITH (OIDS=FALSE);
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An example:
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package main
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import (
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"database/sql"
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"fmt"
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_ "github.com/bmizerany/pq"
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"time"
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)
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const (
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DB_USER = "postgres"
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DB_PASSWORD = "postgres"
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DB_NAME = "test"
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)
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func main() {
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dbinfo := fmt.Sprintf("user=%s password=%s dbname=%s sslmode=disable",
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DB_USER, DB_PASSWORD, DB_NAME)
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db, err := sql.Open("postgres", dbinfo)
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checkErr(err)
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defer db.Close()
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fmt.Println("# Inserting values")
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var lastInsertId int
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err = db.QueryRow("INSERT INTO userinfo(username,departname,created) VALUES($1,$2,$3) returning uid;", "astaxie", "研发部门", "2012-12-09").Scan(&lastInsertId)
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checkErr(err)
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fmt.Println("last inserted id =", lastInsertId)
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fmt.Println("# Updating")
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stmt, err := db.Prepare("update userinfo set username=$1 where uid=$2")
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checkErr(err)
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res, err := stmt.Exec("astaxieupdate", lastInsertId)
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checkErr(err)
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affect, err := res.RowsAffected()
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checkErr(err)
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fmt.Println(affect, "rows changed")
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fmt.Println("# Querying")
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rows, err := db.Query("SELECT * FROM userinfo")
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checkErr(err)
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for rows.Next() {
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var uid int
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var username string
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var department string
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var created time.Time
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err = rows.Scan(&uid, &username, &department, &created)
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checkErr(err)
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fmt.Println("uid | username | department | created ")
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fmt.Printf("%3v | %8v | %6v | %6v\n", uid, username, department, created)
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}
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fmt.Println("# Deleting")
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stmt, err = db.Prepare("delete from userinfo where uid=$1")
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checkErr(err)
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res, err = stmt.Exec(lastInsertId)
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checkErr(err)
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affect, err = res.RowsAffected()
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checkErr(err)
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fmt.Println(affect, "rows changed")
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}
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func checkErr(err error) {
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if err != nil {
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panic(err)
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}
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}
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Note that PostgreSQL uses the `$1, $2` format instead of the `?` that MySQL uses, and it has a different DSN format in `sql.Open`.
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Another thing is that the Postgres driver does not support `sql.Result.LastInsertId()`.
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So instead of this,
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stmt, err := db.Prepare("INSERT INTO userinfo(username,departname,created) VALUES($1,$2,$3);")
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res, err := stmt.Exec("astaxie", "研发部门", "2012-12-09")
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fmt.Println(res.LastInsertId())
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use `db.QueryRow()` and `.Scan()` to get the value for the last inserted id.
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err = db.QueryRow("INSERT INTO TABLE_NAME values($1) returning uid;", VALUE1").Scan(&lastInsertId)
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fmt.Println(lastInsertId)
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## Links
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- [Directory](preface.md)
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- Previous section: [SQLite](05.3.md)
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- Next section: [Develop ORM based on beedb](05.5.md)
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