PHP database operation skills: How to use the mysqli_fetch_array function to obtain query results

PHP database operation skills: How to use the mysqli_fetch_array function to obtain query results

In PHP database operations, we often need to perform some query operations to obtain data in the database. Using the mysqli_fetch_array function can help us easily obtain query results and process them. This article will introduce how to use the mysqli_fetch_array function and some related tips and precautions.

1. Introduction to mysqli_fetch_array function
The mysqli_fetch_array function is a function provided by PHP for returning query results. It gets the next row from the result set as an associative array or a numeric array, or both, and returns it to the caller. Through this function, we can obtain the values ​​of each field of the query result and perform further operations and processing.

2. Basic usage examples
The following is a basic usage example of using the mysqli_fetch_array function to obtain query results:

<?php
// 连接数据库
$servername = "localhost";
$username = "root";
$password = "password";
$dbname = "myDB";

$conn = mysqli_connect($servername, $username, $password, $dbname);

// 检查连接是否成功
if (!$conn) {
    die("连接失败: " . mysqli_connect_error());
}

// 执行查询语句
$sql = "SELECT id, name, age FROM users";
$result = mysqli_query($conn, $sql);

// 输出数据
while ($row = mysqli_fetch_array($result, MYSQLI_ASSOC)) {
    echo "ID: " . $row["id"] . "，姓名: " . $row["name"] . "，年龄: " . $row["age"] . "<br>";
}

// 关闭连接
mysqli_close($conn);
?>

In the above example, we first connected to the database and executed a query statement to obtain the values ​​of the id, name, and age fields in the user table. Then obtain the results line by line through the while loop and the mysqli_fetch_array function, and output the results in the corresponding format. Finally, remember to close the connection to the database.

3. Parameters of the mysqli_fetch_array function
The first parameter of the mysqli_fetch_array function is the result set object, which is usually the result returned by the mysqli_query function. The second parameter is the return type of the result, which can be MYSQLI_ASSOC, MYSQLI_NUM or MYSQLI_BOTH, representing an associative array, a numeric array or both respectively. The default is MYSQLI_BOTH.

4. Determine whether the query result is empty
In actual development, we often need to determine whether the query result is empty so that we can take appropriate processing based on the result. We can use the mysqli_num_rows function to get the number of rows in the result set and determine whether it is empty. The example is as follows:

<?php
// 连接数据库
// ...

// 执行查询语句
$sql = "SELECT id, name, age FROM users";
$result = mysqli_query($conn, $sql);

// 判断结果是否为空
if (mysqli_num_rows($result) > 0) {
    // 输出数据
    while ($row = mysqli_fetch_array($result, MYSQLI_ASSOC)) {
        // ...
    }
} else {
    echo "查询结果为空！";
}

// 关闭连接
// ...
?>

In the above example, after executing the query statement, we first determine whether the number of rows in the result set is greater than 0. If so, use the mysqli_fetch_array function to obtain the result and process it; if not, then Output a prompt that the query result is empty.

5. Traverse the query results
When we need to get each row of the query results, we can use the mysqli_fetch_all function to return all the results at once and store them in an array. An example is as follows:

<?php
// 连接数据库
// ...

// 执行查询语句
$sql = "SELECT id, name, age FROM users";
$result = mysqli_query($conn, $sql);

// 获取所有结果
$rows = mysqli_fetch_all($result, MYSQLI_ASSOC);

// 遍历结果
foreach ($rows as $row) {
    echo "ID: " . $row["id"] . "，姓名: " . $row["name"] . "，年龄: " . $row["age"] . "<br>";
}

// 关闭连接
// ...
?>

In the above example, we use the mysqli_fetch_all function to store the query results in an array (rows), and then traverse the array through a foreach loop to obtain the data of each row and output it.

6. Summary
This article introduces how to use the mysqli_fetch_array function to obtain query results and process them. By mastering the basic usage and related techniques of this function, we can more flexibly operate database query results and improve development efficiency and code quality. I hope this article will be helpful to readers in their learning and practice of PHP database operations.

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