What are common reasons for the error "mysql_fetch_assoc() expects parameter 1 to be resource, boolean given" in PHP?

The error "mysql_fetch_assoc() expects parameter 1 to be resource, boolean given" typically occurs when the query executed by the `mysql_query()` function fails, returning a boolean value (false) instead of a resource. This can happen due to syntax errors in the SQL query, connection issues, or other database-related problems. To solve this issue, you should check the return value of `mysql_query()` before passing it to `mysql_fetch_assoc()` to ensure it is a valid resource.

$result = mysql_query($query);

if($result === false) {
    // Handle the query error
} else {
    while($row = mysql_fetch_assoc($result)) {
        // Process the fetched data
    }
}