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Go MySQL

last modified September 20, 2020

Go MySQL tutorial shows how to work with MySQL in Golang. The examples perform basic database operations.

MySQL is a leading open source database management system. It is a multi-user, multithreaded database management system. MySQL is especially popular on the web. MariaDB is a community-developed, commercially supported fork of the MySQL relational database management system.

Go has the sql package which provides a generic interface around SQL (or SQL-like) databases. The sql package must be used in conjunction with a database driver.

The package provides automatic connection pooling. Each time we query a database, we are using a connection from a pool of connections that has been set up when the application has started. The connections are reused.

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

We need to install the MySQL driver.

cities_mysql.sql
USE testdb;
DROP TABLE IF EXISTS cities;
CREATE TABLE cities(id INT PRIMARY KEY AUTO_INCREMENT, name VARCHAR(255), population INT);
INSERT INTO cities(name, population) VALUES('Bratislava', 432000);
INSERT INTO cities(name, population) VALUES('Budapest', 1759000);
INSERT INTO cities(name, population) VALUES('Prague', 1280000);
INSERT INTO cities(name, population) VALUES('Warsaw', 1748000);
INSERT INTO cities(name, population) VALUES('Los Angeles', 3971000);
INSERT INTO cities(name, population) VALUES('New York', 8550000);
INSERT INTO cities(name, population) VALUES('Edinburgh', 464000);
INSERT INTO cities(name, population) VALUES('Berlin', 3671000);

In the tutorial, we use the cities table.

Go MySQL version

In the first example, we print the version of MySQL.

version.go
package main

import (
    "database/sql"
    "fmt"
    "log"

    _ "github.com/go-sql-driver/mysql"
)

func main() {

    db, err := sql.Open("mysql", "user7:s$cret@tcp(127.0.0.1:3306)/testdb")
    defer db.Close()

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

    var version string

    err2 := db.QueryRow("SELECT VERSION()").Scan(&version)

    if err2 != nil {
        log.Fatal(err2)
    }

    fmt.Println(version)
}

The program returns the version of MySQL. The version is determined by executing the SELECT VERSION() statement.

_ "github.com/go-sql-driver/mysql"

When a package is imported prefixed with a blank identifier, the init function of the package is called. The function registers the driver.

db, err := sql.Open("mysql", "user7:s$cret@tcp(127.0.0.1:3306)/testdb")

With sql.Open, we open a database specified by its database driver name and a driver-specific data source name, usually consisting of at least a database name and connection information. It does not establish any connections to the database, nor does it validate driver connection parameters. Instead, it simply prepares the database abstraction for later use. The first actual connection to the underlying datastore will be established lazily, when it's needed for the first time.

defer db.Close()

The Close returns the connection to the connection pool. It is idiomatic to defer db.Close if the sql.DB should not have a lifetime beyond the scope of the function.

err2 := db.QueryRow("SELECT VERSION()").Scan(&version)

The QueryRow executes a query that is expected to return at most one row. The Scan function copies the column from the matched row into the version variable.

$ go run version.go
10.3.24-MariaDB-2

This is a sample output.

Go MySQL select all rows with Query

The Query executes a query that returns rows, typically a SELECT. The optional arguments are for any placeholder parameters in the query.

select_all.go
package main

import (
    "database/sql"
    "fmt"
    "log"

    _ "github.com/go-sql-driver/mysql"
)

type City struct {
    Id         int
    Name       string
    Population int
}

func main() {

    db, err := sql.Open("mysql", "user7:s$cret@tcp(127.0.0.1:3306)/testdb")
    defer db.Close()

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

    res, err := db.Query("SELECT * FROM cities")

    defer res.Close()

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

    for res.Next() {

        var city City
        err := res.Scan(&city.Id, &city.Name, &city.Population)

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

        fmt.Printf("%v\n", city)
    }
}

The example prints all rows from the cities table.

for res.Next() {

The Next prepares the next result row for reading with the Scan method. It returns true on success, or false if there is no next result row or an error happened while preparing it.

err := res.Scan(&city.Id, &city.Name, &city.Population)

We read the data into the City structure Scan.

$ go run select_all.go
{1 Bratislava 432000}
{2 Budapest 1759000}
{3 Prague 1280000}
{4 Warsaw 1748000}
{5 Los Angeles 3971000}
{6 New York 8550000}
{7 Edinburgh 464000}
{8 Berlin 3671000}

This is the output.

Go MySQL insert row with Exec

The Exec function executes a query without returning any rows. It is used with INSERT, UPDATE, DELETE, or DROP statements. The optional arguments are for any placeholder parameters in the query.

insert_row.go
package main

import (
    "database/sql"
    "fmt"
    "log"

    _ "github.com/go-sql-driver/mysql"
)

func main() {

    db, err := sql.Open("mysql", "user7:s$cret@tcp(127.0.0.1:3306)/testdb")
    defer db.Close()

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

    sql := "INSERT INTO cities(name, population) VALUES ('Moscow', 12506000)"
    res, err := db.Exec(sql)

    if err != nil {
        panic(err.Error())
    }

    lastId, err := res.LastInsertId()

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

    fmt.Printf("The last inserted row id: %d\n", lastId)
}

The example inserts a new row into the cities table.

sql := "INSERT INTO cities(name, population) VALUES ('Moscow', 12506000)"
res, err := db.Exec(sql)

We insert a new city into the table.

lastId, err := res.LastInsertId()

With LastInsertId, we get the last inserted id.

Go MySQL prepared statement

With prepared statements, we use placeholders instead of directly writing the values into the statements. Prepared statements increase security and performance of database operations.

Go creates prepared statements for you under the covers.

db.Query(sql, param1, param2)

The Query function prepares the SQL, then executes it with the parameters and finally closes the statement.

prepared.go
package main

import (
    "database/sql"
    "fmt"
    "log"

    _ "github.com/go-sql-driver/mysql"
)

type City struct {
    Id         int
    Name       string
    Population int
}

func main() {

    db, err := sql.Open("mysql", "user7:s$cret@tcp(127.0.0.1:3306)/testdb")
    defer db.Close()

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

    var myid int = 1

    res, err := db.Query("SELECT * FROM cities WHERE id = ?", myid)
    defer res.Close()

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

    if res.Next() {

        var city City
        err := res.Scan(&city.Id, &city.Name, &city.Population)

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

        fmt.Printf("%v\n", city)
    } else {

        fmt.Println("No city found")
    }
}

The example selects a row from the database.

res, err := db.Query("SELECT * FROM cities WHERE id = ?", myid)

The ? is a placeholder which is filled with the value from the myid variable. Under the hood, db.Query actually prepares, executes, and closes a prepared statement.

$ go run prepared.go
{1 Bratislava 432000}

This is the output.

Go MySQL affected rows

The RowsAffected returns the number of rows affected by an update, insert, or delete statements.

affected_rows.go
package main

import (
    "database/sql"
    "fmt"
    "log"

    _ "github.com/go-sql-driver/mysql"
)

func main() {

    db, err := sql.Open("mysql", "user7:s$cret@tcp(127.0.0.1:3306)/testdb")
    defer db.Close()

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

    sql := "DELETE FROM cities WHERE id IN (2, 4, 6)"
    res, err := db.Exec(sql)

    if err != nil {
        panic(err.Error())
    }

    affectedRows, err := res.RowsAffected()

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

    fmt.Printf("The statement affected %d rows\n", affectedRows)
}

In the example, we delete three rows with a DELETE SQL statement. Then we print the number of deleted rows with RowsAffected.

$ go run affected_rows.go 
The statement affected 3 rows

This is the output.

In this tutorial, we have worked with MySQL in Go.

List all Go tutorials.