How to query a MySQL database using PHP

As a developer, we will inevitably come into contact with database applications at work. As for the language that completes database operations, PHP is undoubtedly the most widely used language. In PHP, using the MySQL database is one of the most common practices. This article mainly explains how to use PHP to query the MySQL database and gives the corresponding source code.

[Database Query]

First of all, we need to understand what a database query is. In MySQL, a query is an operation used to retrieve data from a database. Through queries, we can obtain the data stored in the database and use it for subsequent operations. Therefore, it is very necessary to know how to query the database.

In PHP, the process of querying the database is very simple. We only need to use some specific functions in the PHP program to query the data in the database. Next, let’s take a look at the specific steps.

[Steps]

1. Connect to MySQL database

In PHP, we connect to MySQL database through two extensions, MySQLi and PDO. This article mainly uses the MySQLi extension to operate. The steps to connect to the MySQL database are as follows:

$servername = "localhost"; // 数据库所在服务器的名称
$username = "username"; // 用户名
$password = "password"; // 密码
$dbname = "myDB"; // 数据库名称

// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);

// 检查连接是否正常
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

The above code uses the mysqli_connect() function to create a connection. When the connection fails, we use the die() function to output an error message and stop the execution of the program.

2. Execute query

After the connection is successful, we can start executing the query. In PHP, we use mysqli_query() function to execute queries. The following is an example of querying all data:

$sql = "SELECT * FROM MyGuests";
$result = $conn->query($sql);

In the above code, we use the SELECT statement to select all the data in the MyGuests table and save the results in the $result variable.

3. Processing query results

The result of the query is usually a list containing multiple rows of data, and we need to process it row by row. The following is an example of traversing the query results and printing:

if ($result->num_rows > 0) {
    // 输出数据
    while($row = $result->fetch_assoc()) {
        echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>";
    }
} else {
    echo "0 结果。";
}

In the above code, we use the if statement to check whether the result list is empty. If it's not empty, use a while loop to iterate through the result list and print each row of data.

4. Close the connection

When the query ends, we need to close the database connection. The following is the code to close the connection:

$conn->close();

[Source code]

The following is the complete code snippet for querying all data in the MyGuests table.

connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 执行查询
$sql = "SELECT * FROM MyGuests";
$result = $conn->query($sql);

// 处理查询结果
if ($result->num_rows > 0) {
    // 输出数据
    while($row = $result->fetch_assoc()) {
        echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>";
    }
} else {
    echo "0 结果。";
}

// 关闭连接
$conn->close();
?>

[Summary]

In this article, we learned how to use PHP to query the MySQL database and provided the corresponding source code. Whether you are a novice or an experienced user, I hope this article will be helpful to your database query operations.

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