如果该位的值为 1 并且第一个字符串为 NULL，MySQL MAKE_SET() 函数返回什么？
示例
mysql> Select MAKE_SET(1, NULL,'A','B'); +---------------------------+ | MAKE_SET(1, NULL,'A','B') | +---------------------------+ | | +---------------------------+ 1 row in set (0.00 sec)登录后复制
示例
mysql> Select MAKE_SET(1, NULL,'A','B'); +---------------------------+ | MAKE_SET(1, NULL,'A','B') | +---------------------------+ | | +---------------------------+ 1 row in set (0.00 sec)登录后复制
