如果任何参数为NULL，则哪个MySQL EXPORT_SET()函数返回？
如果MySQLEXPORT_SET()函数提供的任何参数为NULL，则它将返回NULL。以下示例将演示它-
示例
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)