PHP Warning: mysql_num_rows() expects parameter 1 to be resource solution

Solution to PHP Warning: mysql_num_rows() expects parameter 1 to be resource

When you are writing code in PHP, if "PHP Warning: mysql_num_rows() expects parameter 1 to be resource" appears This warning indicates that the first parameter of the mysql_num_rows() function is not set correctly. In this article, we'll cover how to fix this problem to ensure your PHP code runs properly.

First, let us understand the mysql_num_rows() function. The function of this function is to return the number of rows in the query result set. It requires a query result set as the first parameter. If this parameter is incorrect, the above warning will appear.

There are many possible reasons for this warning. The following are some common reasons:

1. The database connection failed.
2. Database query failed.
3. The query result set is empty.

Next, we will discuss these reasons one by one and introduce how to solve them.

1. Database connection failure

This warning will appear if you do not connect to the database correctly before using the mysql_num_rows() function. To resolve this issue, you need to make sure you are using the correct database connection functions. For example, if you are using a MySQL database, you need to use the mysql_connect() function to connect to the database.

The following is a sample code to connect to a MySQL database:

$servername = "localhost"; // 数据库服务器名
$username = "用户名"; // 数据库用户名
$password = "密码"; // 数据库密码
$dbname = "数据库名"; // 数据库名

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

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

// 选择数据库
mysql_select_db($dbname, $conn);

2. Database query failed

If your database query fails, it will also cause mysql_num_rows( ) function fails. To solve this problem, you need to check whether your query statement is correct and whether you have sufficient permissions to access the tables in the database.

The following is a sample code for the mysql_query() function:

$sql = "SELECT * FROM users";
$result = mysql_query($sql, $conn);

if (!$result) {
    die("查询失败: " . mysql_error());
}

$num_rows = mysql_num_rows($result);

3. The query result set is empty

If the query result set is empty, it will also cause mysql_num_rows() Function failed. To solve this problem, you can use the mysql_fetch_array() function to determine whether any rows have been returned. The following is a sample code for the mysql_fetch_array() function:

$sql = "SELECT * FROM users";
$result = mysql_query($sql, $conn);

if (!$result) {
    die("查询失败: " . mysql_error());
}

$row = mysql_fetch_array($result);

if ($row) {
    $num_rows = mysql_num_rows($result);
} else {
    echo "没有结果";
}

In summary, when you use the mysql_num_rows() function, if "PHP Warning: mysql_num_rows() expects parameter 1 to be resource" appears Warning, it may be that your database connection failed, the query failed, or the query result set is empty. The best way to solve this problem is to double-check your codes and make sure they are correct.

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