Why Does `mysqli_num_rows()` Return a 'boolean given' Error in PHP and MySQL?

PHP & MySQL: Resolving mysqli_num_rows() Parameter Error with mysqli_result

When integrating HTML Purifier into PHP for data validation, it's crucial to ensure proper parameter passing to avoid common errors like "mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given."

Understanding the Error

Typically, this error occurs when the mysqli_num_rows() function is called with an incorrect argument. It expects a valid mysqli_result object as its first parameter. In the given code snippet, the first parameter is $dbc, which needs to be a valid result set from a MySQL query.

Possible Causes

Incorrect usage or a malformed query can lead to a boolean value (FALSE) being returned instead of a mysqli_result object. This can happen if:

• The query syntax has an error.
• The mysqli_query() function is not properly executed.
• The query returns an empty result set.

Resolving the Issue

In the provided code, the issue lies within the SQL query used to retrieve data from the database:

$dbc = mysqli_query($mysqli,"SELECT users.*, profile.*
                                 FROM users 
                                 INNER JOIN contact_info ON contact_info.user_id = users.user_id 
                                 WHERE users.user_id=3");

The error is caused by the omission of the join with profile in comparison to users and contact_info. The correct query should be:

$dbc = mysqli_query($mysqli,"SELECT u.*, p.*
                                 FROM users AS u
                                 LEFT JOIN profile AS p ON u.user_id = p.user_id
                                 WHERE u.user_id=3");

By fixing the query, the $dbc variable will return a valid mysqli_result object, enabling you to use mysqli_num_rows() effectively:

if (mysqli_num_rows($dbc) == 0) {
        //...

The above is the detailed content of Why Does `mysqli_num_rows()` Return a 'boolean given' Error in PHP and MySQL?. For more information, please follow other related articles on the PHP Chinese website!