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5.4 PostgreSQL

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 as an alternative to Oracle. Postgresql is a good choice for enterprise type projects.

PostgreSQL drivers

There are many database drivers available for PostgreSQL. Here are three examples of them:

I will use the first one in the examples that follow.

Samples

We create the following SQL:

CREATE TABLE userinfo
(
    uid serial NOT NULL,
    username character varying(100) NOT NULL,
    departname character varying(500) NOT NULL,
    Created date,
    CONSTRAINT userinfo_pkey PRIMARY KEY (uid)
)
WITH (OIDS=FALSE);

An example:

package main

import (
	"database/sql"
	"fmt"
	_ "github.com/lib/pq"
	"time"
)

const (
	DB_USER     = "postgres"
	DB_PASSWORD = "postgres"
	DB_NAME     = "test"
)

func main() {
	dbinfo := fmt.Sprintf("user=%s password=%s dbname=%s sslmode=disable",
		DB_USER, DB_PASSWORD, DB_NAME)
	db, err := sql.Open("postgres", dbinfo)
	checkErr(err)
	defer db.Close()

	fmt.Println("# Inserting values")

	var lastInsertId int
	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)
	checkErr(err)
	fmt.Println("last inserted id =", lastInsertId)

	fmt.Println("# Updating")
	stmt, err := db.Prepare("update userinfo set username=$1 where uid=$2")
	checkErr(err)

	res, err := stmt.Exec("astaxieupdate", lastInsertId)
	checkErr(err)

	affect, err := res.RowsAffected()
	checkErr(err)

	fmt.Println(affect, "rows changed")

	fmt.Println("# Querying")
	rows, err := db.Query("SELECT * FROM userinfo")
	checkErr(err)

	for rows.Next() {
		var uid int
		var username string
		var department string
		var created time.Time
		err = rows.Scan(&uid, &username, &department, &created)
		checkErr(err)
		fmt.Println("uid | username | department | created ")
		fmt.Printf("%3v | %8v | %6v | %6v\n", uid, username, department, created)
	}

	fmt.Println("# Deleting")
	stmt, err = db.Prepare("delete from userinfo where uid=$1")
	checkErr(err)

	res, err = stmt.Exec(lastInsertId)
	checkErr(err)

	affect, err = res.RowsAffected()
	checkErr(err)

	fmt.Println(affect, "rows changed")
}

func checkErr(err error) {
	if err != nil {
		panic(err)
	}
}

Note that PostgreSQL uses the $1, $2 format instead of the ? that MySQL uses, and it has a different DSN format in sql.Open. Another thing is that the PostgreSQL driver does not support sql.Result.LastInsertId(). So instead of this,

stmt, err := db.Prepare("INSERT INTO userinfo(username,departname,created) VALUES($1,$2,$3);")
res, err := stmt.Exec("astaxie", "研发部门", "2012-12-09")
fmt.Println(res.LastInsertId())

use db.QueryRow() and .Scan() to get the value for the last inserted id.

err = db.QueryRow("INSERT INTO TABLE_NAME values($1) returning uid;",	VALUE1").Scan(&lastInsertId)
fmt.Println(lastInsertId)

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