MySQL CONCAT() function will return a NULL if you will add a NULL value while linking two strings. Following example will demonstrate it −
Example
mysql> Select CONCAT('Tutorials',NULL,'Point'); +----------------------------------+ | CONCAT('Tutorials',NULL,'Point') | +----------------------------------+ | NULL | +----------------------------------+ 1 row in set (0.06 sec) mysql> Select CONCAT('TutorialsPoint','.com',NULL); +--------------------------------------+ | CONCAT('TutorialsPoint','.com',NULL) | +--------------------------------------+ | NULL | +--------------------------------------+ 1 row in set (0.00 sec)