What potential error can occur when using mysql_num_rows() in PHP without passing the result variable?

When using mysql_num_rows() in PHP without passing the result variable, it can result in a warning or error because the function expects a valid result set as an argument. To solve this issue, you need to make sure to pass the result variable obtained from the MySQL query to mysql_num_rows(). 

// Incorrect usage without passing the result variable
$num_rows = mysql_num_rows($query);

// Corrected code with passing the result variable
$result = mysql_query("SELECT * FROM table");
$num_rows = mysql_num_rows($result);

Keywords

mysql_num_rows PHP error result variable function

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