How to call MySQL database in php and read query results

PHP is a popular programming language commonly used for dynamic web page programming. As a back-end programming language, PHP is most commonly used to handle database and server-side programming tasks. It's easy to create a connection to a MySQL database using PHP, and it's not difficult to implement basic query functionality. This article will introduce the basic method of using PHP to call the MySQL database and read the query results.

1. Connecting to a MySQL database

Connecting to a MySQL database is easy in PHP. The following is sample code for connecting to a MySQL database using the PHP mysqli database extension.

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

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

// 检查连接是否成功
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
echo "Connected successfully";
?>

In the above example, $servername is the address of the MySQL server, $username and $password are the username and password required to connect to the MySQL database, and $dbname is the name of the database to be connected.

In the error message returned by the connect_error() method, developers can easily find the source of the error to solve the problem faster.

2. Query MySQL database

After connecting to the MySQL database, we need to use SQL query to obtain the required data. The following is a basic SQL query example.

SELECT * FROM mytable WHERE column1 = 'value1'

This query will select all rows from the mytable table where the value of column1 is value1.

Use the mysqli_query() function in PHP to execute queries and obtain results. The following is an example of PHP code that queries a MySQL database.

$sql = "SELECT * FROM mytable WHERE column1 = 'value1'";
$result = mysqli_query($conn, $sql);

if (mysqli_num_rows($result) > 0) {
    // 输出每一行数据
    while($row = mysqli_fetch_assoc($result)) {
        echo "id: " . $row["id"]. " - Name: " . $row["name"]. " - Email: " . $row["email"]. "<br>";
    }
} else {
    echo "0 结果";
}

In the above example, the mysqli_fetch_assoc() function is used to fetch each row of data from the result set. Use a while loop to output each row of data.

3. Close the database connection

After finishing, it is important to close the connection to the MySQL database. In PHP, this can be done using the mysqli_close() function. Below is a sample PHP code.

mysqli_close($conn);

The above is the basic knowledge of MySQL database query based on PHP. Developers can write more complex query code based on their needs. Typically, developers need to consider fully validating user input at query time to prevent SQL injection attacks.

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