Why Does `mysql_fetch_array()` Show 'expects parameter 1 to be resource' and How Can I Fix It?

Understanding the "mysql_fetch_array()/mysql_fetch_assoc()/mysql_fetch_row()/mysql_num_rows etc... expects parameter 1 to be resource" Error

When you encounter this error, it indicates that one of the database retrieval functions (e.g., mysql_fetch_array(), mysql_fetch_assoc(), etc.) is being called with an invalid parameter. Specifically, the parameter should be a resource representing a database result set, but it is instead a boolean value.

The Cause of the Error

The root cause of this error is typically a failed database query. When a query fails, the mysql_* functions/methods return false, which can be misinterpreted as a boolean value. As a result, when you subsequently call a retrieval function with the false result, it leads to this error.

Fixing the Error

To resolve this issue, you must follow these steps:

1. Check the Query Result: Verify that the mysql_query() call does not return false by checking its result.
2. Handle Query Failures: If the query does fail, trigger an error or handle it appropriately.
3. Ensure Proper Parameter: Pass the correct result resource to the retrieval function rather than the boolean value that resulted from the failed query.

Example

Consider the following code:

$username = mysql_real_escape_string($_POST['username']);
$password = $_POST['password'];
$result = mysql_query("SELECT * FROM Users WHERE UserName LIKE '$username'");

if($result === FALSE) {
    trigger_error(mysql_error(), E_USER_ERROR);
}

while($row = mysql_fetch_array($result)) {
    echo $row['FirstName'];
}

In this example, we first check the result of mysql_query() and trigger an error if the query fails. Then, we correctly pass the $result resource to the mysql_fetch_array() function. This ensures that the appropriate parameter is used, preventing the error from occurring.

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