How to query data using PHP

PHP is a popular programming language that helps programmers easily operate databases and query data. In this article, we will learn how to query data using PHP.

First, we need to connect to the database. In PHP, we can use mysqli class or PDO class to connect to the database. Both classes provide methods for creating database connections, such as mysqli_connect() and PDO::__construct().

Next, we need to write the query statement. A query statement describes the data we wish to retrieve from the database. The query statement usually includes the following parts:

1. SELECT clause - specifies the columns to be retrieved
2. FROM clause - specifies the table to be retrieved
3. WHERE clause - Conditions for filtering results

For example, the following is a simple query that will retrieve all records in the "users" table:

SELECT * FROM users;

You can use mysqli_query() or PDO:: The query() method sends a query to the database and gets the returned data from the result set. The following is an example using mysqli:

// 建立数据库连接
$conn = mysqli_connect('localhost', 'username', 'password', 'database');

// 执行查询
$result = mysqli_query($conn, 'SELECT * FROM users');

// 输出结果
while ($row = mysqli_fetch_assoc($result)) {
    var_dump($row);
}

// 关闭数据库连接
mysqli_close($conn);

In the above example, we have used the mysqli_connect() method to connect to the database and the mysqli_query() method to send the query to the database. We use the mysqli_fetch_assoc() method to get a row of data from the result set and the var_dump() method to output the data to the screen. After we complete the query, we close the database connection using the mysqli_close() method.

The following is an example of using PDO:

// 建立数据库连接
$conn = new PDO('mysql:host=localhost;dbname=database', 'username', 'password');

// 执行查询
$result = $conn->query('SELECT * FROM users');

// 输出结果
while ($row = $result->fetch(PDO::FETCH_ASSOC)) {
    var_dump($row);
}

// 关闭数据库连接
$conn = null;

In the above example, we used the PDO::__construct() method to connect to the database and PDO::query() Method sends the query to the database. We use the fetch() method to get a row of data from the result set and the var_dump() method to output the data to the screen. After we complete the query, we close the database connection with a null value.

In short, querying data using PHP is very simple. We just need to connect to the database, write the query statement, send the query and get the data from the result set. Whether you are using mysqli or PDO, you can use PHP to query your database and retrieve data easily.

The above is the detailed content of How to query data using PHP. For more information, please follow other related articles on the PHP Chinese website!