How to use foreach in php to traverse query results

In PHP development, we often need to use a foreach loop to traverse arrays or objects and operate on each of their elements. When we need to get data from the database and need to process them, we can also use a foreach loop to iterate through the query results.

In PHP, we use MySQLi or PDO extension to connect to the database and execute SQL queries. The query result is usually an array or object that contains the data we need. Before using the foreach loop to iterate over the query results, we need to ensure that the format of the query results is correct.

When using the MySQLi extension to connect to the database, we can obtain query results through the mysqli_fetch_array() or mysqli_fetch_object() function. The sample code is as follows:

// 连接数据库
$conn = mysqli_connect($servername, $username, $password, $dbname);

// 执行 SQL 查询
$result = mysqli_query($conn, "SELECT * FROM students");

// 遍历查询结果
while ($row = mysqli_fetch_array($result)) {
    echo $row['id'] . " " . $row['name'] . "<br>";
}

// 关闭数据库连接
mysqli_close($conn);

In this sample code, we first connected to the MySQL database, and then executed a SELECT query statement to obtain all the data in the students table. Next, we use a while loop to iterate through the query results, where the $row variable represents the element of each query result. Inside the loop, we access the id and name properties of each element via the array key and output them to the browser. Finally, we close the database connection and release the resources.

When using PDO extension to connect to the database, we can obtain the query results through the fetch() method of the PDOStatement object. The sample code is as follows:

// 连接数据库
$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);

// 执行 SQL 查询
$result = $conn->query("SELECT * FROM students");

// 遍历查询结果
foreach ($result as $row) {
    echo $row['id'] . " " . $row['name'] . "<br>";
}

// 关闭数据库连接
$conn = null;

In this sample code, we first connected to the MySQL database, and then executed a SELECT query statement to obtain all the data in the students table. Next, we use a foreach loop to iterate over the query results, where the $row variable represents the element of each query result. Inside the loop, we access the id and name properties of each element via the array key and output them to the browser. Finally, we close the database connection and release the resources.

It should be noted that when we traverse the query results, we need to access the value of each element through the attribute name or index of the query result. When using a foreach loop, we need to iterate the query results as an array; when using a while loop, we need to use the mysqli_fetch_array() function to convert the query results into an array.

In short, using foreach to loop through query results is a very practical technique in PHP development. By properly applying this technique, we can more easily process and manage the data obtained from the database, and improve the reusability and maintainability of the code.

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