How to replace database in PHP

PHP database replacement - simple and easy-to-understand tutorial

During the development process, we often encounter situations where the database needs to be updated. However, when going through this process, few people think about replacing the database. However, if you want to change your database, you may encounter some difficulties, especially if you want to use a different database management system. In this article, we will discuss how to replace a database in PHP.

1. Choose a new database management system

In PHP, we can use a variety of database management systems. For example: MySQL, PostgreSQL and SQLite, etc. However, please note that when choosing your new database, choose one that suits your needs and the type of data storage. Because different databases have different performance and uses.

2. Establish a new database connection

After selecting a new database, we need to establish a new database connection in order to use it in the application. We can connect to different databases using PDO object or mysqli object in PHP. Before connecting to a new database, make sure your server has the database of your choice installed and that you have permission to connect (username password). The following is the sample code:

Connect using PDO:

$dsn = 'mysql:host=localhost;dbname=test';
$username = 'root';
$password = '';
$options = array(
    PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8'
);
$pdo = new PDO($dsn, $username, $password, $options);

Connect using Mysqli:

$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// 创建连接
$conn = mysqli_connect($servername, $username, $password, $dbname);
// 检测连接
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
echo "Connected successfully";

3. Open the old database connection

Before connecting to the new database , we need to open the old database connection to read data from the old data. We can connect to the old database using PDO or mysqli. The following is the sample code:

Connect using PDO:

$dsn = 'mysql:host=localhost;dbname=old_db';
$username = 'root';
$password = '';
$options = array(
    PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8'
);
$pdo_old = new PDO($dsn, $username, $password, $options);

Connect using Mysqli:

$servername_old = "localhost";
$username_old = "username";
$password_old = "password";
$dbname_old = "myDB_old";

// 创建连接
$conn_old = mysqli_connect($servername_old, $username_old, $password_old, $dbname_old);
// 检测连接
if (!$conn_old) {
    die("Connection failed: " . mysqli_connect_error());
}
echo "Connected successfully";

4. Select data from the old database

In the old database After the connection is successful, we can use SQL statements to select data from the old data. The data will be copied to the new database. For example, we want to select all data from the "users" table in the old database. The following is the sample code:

Using PDO:

$old_users = $pdo_old->query("SELECT * FROM users")->fetchAll(PDO::FETCH_ASSOC);

Using Mysqli:

$sql = "SELECT * FROM users";
$result = mysqli_query($conn_old, $sql);

// 输出每行数据
while($row = mysqli_fetch_assoc($result)) {
    echo "id: " . $row["id"]. " - Name: " . $row["name"]. " " . $row["email"]. "<br>";
}

5. Write to the new database

Now, we can The selected data is written to the new database. We need to use SQL statements to write data to the new database table. During this process, we need to pay attention to the fact that the fields of the new and old database tables are the same, and the data types must match. The following is the sample code:

Using PDO:

$pdo->beginTransaction();
foreach ($old_users as $old_user) {
    $stmt = $pdo->prepare("
         INSERT INTO users 
         (id, name, email) 
         VALUES (:id, :name, :email)
    ");
    $stmt->bindParam(':id', $old_user['id'], PDO::PARAM_INT);
    $stmt->bindParam(':name', $old_user['name'], PDO::PARAM_STR);
    $stmt->bindParam(':email', $old_user['email'], PDO::PARAM_STR);
    $stmt->execute();
}
$pdo->commit();

Using Mysqli:

$sql = "INSERT INTO users (id, name, email)
VALUES ('1', 'John', 'john@example.com')";
if (mysqli_query($conn, $sql)) {
    echo "New record created successfully";
} else {
    echo "Error: " . $sql . "<br>" . mysqli_error($conn);
}

6. Delete the old data

Copy the data from the old database Once in the new database, we should delete the data in the old database that is no longer needed. We can use DELETE statement to delete all data or specific rows in a table. Here is the sample code:

Using PDO:

$pdo_old->exec("DELETE FROM users");

Using Mysqli:

$sql = "DELETE FROM users";
if (mysqli_query($conn_old, $sql)) {
    echo "Record deleted successfully";
} else {
    echo "Error deleting record: " . mysqli_error($conn_old);
}

Conclusion

In PHP, with this simple tutorial, you can Better understand how to replace the database. Although this operation may cause you some trouble, if you follow the above steps, there will basically be no problems.

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