How does PHP control the database for addition, deletion, modification and query operations?

With the development of the Internet, databases have become an indispensable part of modern information systems, and addition, deletion, modification and query operations on databases have become more and more common. In this article, we will introduce how to use PHP language to complete the addition, deletion, modification and query operations of the database, and demonstrate the specific operations through examples.

1. Establishment of database connection

In PHP, we can use mysqli or PDO class to connect to the database. In this article we will use mysqli to implement it.

1. Connect to the database

Before performing any database operation, a connection needs to be established. Use the mysqli_connect method to establish a connection, which requires four parameters:

$servername = "localhost";  // 服务器名称
$username = "your_username"; // 数据库用户名
$password = "your_password"; // 数据库密码
$dbname = "your_dbname"; // 数据库名称

$conn = mysqli_connect($servername, $username, $password, $dbname);

if (!$conn) {
  die("Connection failed: " . mysqli_connect_error());
}

2. Close the database connection

After completing the database operation, the database connection must be closed to avoid wasting resources. We can use the mysqli_close method to close the connection:

mysqli_close($conn);

2. Add, delete, modify and query operations in the database

1. Add data

To add data in the database, you need to use SQL statements INSERT INTO. The mysqli_query method can be used in PHP to perform INSERT INTO operations. The following is an example:

$sql = "INSERT INTO users (firstname, lastname, email) VALUES ('John', 'Doe', 'john@example.com')";

if (mysqli_query($conn, $sql)) {
  echo "New record created successfully";
} else {
  echo "Error: " . $sql . "
" . mysqli_error($conn);
}

2. Delete data

To delete data in the database, you need to use the SQL statement DELETE. You can use the mysqli_query method in PHP to perform DELETE operations. The following is an example:

$sql = "DELETE FROM users WHERE id=1";

if (mysqli_query($conn, $sql)) {
  echo "Record deleted successfully";
} else {
  echo "Error deleting record: " . mysqli_error($conn);
}

3. Update data

To update data in the database, you need to use the SQL statement UPDATE. The mysqli_query method can be used in PHP to perform UPDATE operations. The following is an example:

$sql = "UPDATE users SET lastname='Doe', email='john@example.com' WHERE id=1";

if (mysqli_query($conn, $sql)) {
  echo "Record updated successfully";
} else {
  echo "Error updating record: " . mysqli_error($conn);
}

4. Query data

To query data in the database, you need to use the SQL statement SELECT. The mysqli_query method can be used in PHP to perform SELECT operations. The following is an example:

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

if (mysqli_num_rows($result) > 0) {
  while($row = mysqli_fetch_assoc($result)) {
    echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "
";
  }
} else {
  echo "0 results";
}

The above code will return all the data in the users data table, and traverse the output results through a while loop.

3. Summary

In this article, we learned how to use mysqli to connect to the database and implement the addition, deletion, modification and query operations of the database. For PHP beginners, these operations are very basic knowledge points, but they must also be mastered, because no matter which website you build, you need to interact with the database. A thorough understanding and mastery of these operations can lay a solid foundation for writing more efficient programs, optimizing database performance, and improving user experience.

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