방문 조리 시스템에서 사용자 계정 관리 모듈을 Go 언어를 사용하여 작성하는 방법은 무엇입니까?

CREATE TABLE user (
    id INT PRIMARY KEY AUTO_INCREMENT,
    username VARCHAR(50) NOT NULL,
    password VARCHAR(100) NOT NULL,
    email VARCHAR(100) NOT NULL
);

package main

import (
    "database/sql"
    "fmt"

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

type User struct {
    ID       int
    Username string
    Password string
    Email    string
}

func connectDB() (*sql.DB, error) {
    db, err := sql.Open("mysql", "username:password@tcp(host:port)/database")
    if err != nil {
        return nil, err
    }
    return db, nil
}

func createUser(user User) error {
    db, err := connectDB()
    if err != nil {
        return err
    }
    defer db.Close()

    _, err = db.Exec("INSERT INTO user (username, password, email) VALUES (?, ?, ?)",
        user.Username, user.Password, user.Email)
    if err != nil {
        return err
    }
    return nil
}

func getUserByUsername(username string) (User, error) {
    db, err := connectDB()
    if err != nil {
        return User{}, err
    }
    defer db.Close()

    var user User
    err = db.QueryRow("SELECT id, username, password, email FROM user WHERE username = ?", username).
        Scan(&user.ID, &user.Username, &user.Password, &user.Email)
    if err != nil {
        return User{}, err
    }
    return user, nil
}

func updateUser(user User) error {
    db, err := connectDB()
    if err != nil {
        return err
    }
    defer db.Close()

    _, err = db.Exec("UPDATE user SET username = ?, password = ?, email = ? WHERE id = ?",
        user.Username, user.Password, user.Email, user.ID)
    if err != nil {
        return err
    }
    return nil
}

func deleteUser(id int) error {
    db, err := connectDB()
    if err != nil {
        return err
    }
    defer db.Close()

    _, err = db.Exec("DELETE FROM user WHERE id = ?", id)
    if err != nil {
        return err
    }
    return nil
}

func main() {
    // 创建用户账户
    user := User{
        Username: "john",
        Password: "123456",
        Email:    "john@example.com",
    }
    err := createUser(user)
    if err != nil {
        fmt.Println(err)
        return
    }

    // 根据用户名查询用户账户
    retrievedUser, err := getUserByUsername("john")
    if err != nil {
        fmt.Println(err)
        return
    }
    fmt.Println(retrievedUser)

    // 更新用户账户
    retrievedUser.Username = "john2"
    err = updateUser(retrievedUser)
    if err != nil {
        fmt.Println(err)
        return
    }

    // 删除用户账户
    err = deleteUser(retrievedUser.ID)
    if err != nil {
        fmt.Println(err)
        return
    }
}