MySQL EXPORT_SET() function would return NULL if any of the argument provided in it is NULL. Following examples would demonstrate it −
Example
mysql> Select EXPORT_SET(NULL, 'Y','N',',', 4); +----------------------------------+ | EXPORT_SET(NULL, 'Y','N',',', 4) | +----------------------------------+ | NULL | +----------------------------------+ 1 row in set (0.00 sec) mysql> Select EXPORT_SET(5, NULL,'N',',', 4); +--------------------------------+ | EXPORT_SET(5, NULL,'N',',', 4) | +--------------------------------+ | NULL | +--------------------------------+ 1 row in set (0.00 sec) mysql> Select EXPORT_SET(5, 'Y','N',',', NULL); +----------------------------------+ | EXPORT_SET(5, 'Y','N',',', NULL) | +----------------------------------+ | NULL | +----------------------------------+ 1 row in set (0.00 sec) mysql> Select EXPORT_SET(5, 'Y','N',NULL, 4); +--------------------------------+ | EXPORT_SET(5, 'Y','N',NULL, 4) | +--------------------------------+ | NULL | +--------------------------------+ 1 row in set (0.00 sec)