$wpdb – what does it return on fail?

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I’m not sure whether this question is WordPress specific or is more related to mySQL. I am trying to find out what would be returned if the transaction with the database fails.
In the following scenario, I am updating a row. If none of the values are changed false is returned. If changes are made true is returned. How can I tell if the transaction has failed? 

$result = $wpdb->update($this->table_name, $dbfields, $where);
if($result == false)//do fail - this is not really a fail!
if($result == true)//do success

Any pointers appreciated.

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  1. Take a look in wp-includeswp-db.php. The header comments of wpdb’s update function says:

     * @return int|false The number of rows updated, or false on error.

    So, I’d suspect that you want to find the difference between false (a boolean value indicating a failure) and 0 (an integer indicating that no rows were returned.)

    If you compare using ==, false and 0 are equal. You therefore need to use the === operator to check whether you’re dealing with the boolean false or the integer 0.

    So, try these:

    if ($result === false) // Fail -- the "===" operator compares type as well as value
if ($result === 0) // Success, but no rows were updated
if ($result > 0) // Success, and updates were done. $result is the number of affected rows.

    See the PHP manual for more information on the === comparison operator.