MySQL MAKE_SET()函数何时返回NULL？
如果该位的值为NULL，则MySQLMAKE_SET()函数将返回NULL，否则该函数将忽略其他任何位置的NULL。以下示例将演示它-
示例
mysql> Select MAKE_SET(NULL, 'A','B','C'); +-----------------------------+ | MAKE_SET(NULL, 'A','B','C') | +-----------------------------+ | NULL | +-----------------------------+ 1 row in set (0.00 sec) mysql> Select MAKE_SET(2, NULL,'B',NULL); +----------------------------+ | MAKE_SET(2, NULL,'B',NULL) | +----------------------------+ | B | +----------------------------+ 1 row in set (0.00 sec)