How to query results and assign variables in php

With the advent of the Internet era, many websites have adopted PHP, a programming language, to build and maintain their websites. In the development process of PHP, it is often necessary to query and operate the database and save the query results into variables. This article will introduce specific operating steps and techniques.

1. Connect to the database

In PHP, you first need to connect to the database to query and operate data. Connecting to the database usually uses the mysqli_connect() function or PDO class instantiation.

The usage of mysqli_connect() function is as follows:

 $servername = "localhost";//数据库服务器名称
 $username = "username";//数据库用户名
 $password = "password";//数据库密码
 $dbname = "dbname";//数据库名称
 $conn = mysqli_connect($servername, $username, $password,$dbname);
 
if (!$conn) {
 die("连接失败: " . mysqli_connect_error());
}

The usage of PDO class instantiation method is as follows:

 $servername = "localhost";//数据库服务器名称
 $username = "username";//数据库用户名
 $password = "password";//数据库密码
 $dbname = "dbname";//数据库名称
 try {
    $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
    // 设置 PDO 错误模式为异常
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    echo "连接成功";
    }
catch(PDOException $e)
    {
    echo "连接失败: " . $e->getMessage();
    }

2. Execute the query statement

After the connection is successful, you can start executing the query statement. Query through the mysqli_query() function in PHP or the query() method of the PDO class to obtain the query results.

Mysqli_query() function is used as follows:

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

The query() method of the PDO class is used as follows:

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

3. Assign the query results to Variable

After executing the query statement, the query results can be saved in a variable for subsequent operations, such as display or update, etc.

In PHP, you can convert the query results into the form of an array or associative array through the mysqli_fetch_array() or mysqli_fetch_assoc() function or the fetch() method of the PDO class, and then assign it to a variable.

The use of the mysqli_fetch_array() function is as follows:

while($row = mysqli_fetch_array($result,MYSQLI_ASSOC)) {
    $id = $row['id'];
    $name = $row['name'];
    $age = $row['age'];
}

The use of the mysqli_fetch_assoc() function is as follows:

while($row = mysqli_fetch_assoc($result)) {
   $id = $row["id"];
   $name = $row["name"];
   $age = $row["age"];
}

The use of the fetch() method of the PDO class is as follows Shown:

while($row = $result->fetch(PDO::FETCH_ASSOC)) {
   $id = $row['id'];
   $name = $row['name'];
   $age = $row['age'];
}

4. Close the database connection

After using the database, you need to close the database connection through the mysqli_close() function or the nullify() method of the PDO class to avoid resource loss. Waste and safety issues.

The use of the mysqli_close() function is as follows:

mysqli_close($conn);

The use of the nullify() method of the PDO class is as follows:

$conn = null;

Summary

Through the above introduction, we can find that querying in PHP and assigning the results to variables is an essential step. By calling the corresponding function or class method, we can easily connect to the database and perform query operations.

I hope that the content introduced in this article can help everyone better understand the query operations in PHP so as to better develop and maintain the website.

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