如果 QUOTE() 函数的参数为 NULL，MySQL 将返回 NULL。
示例
mysql> Select QUOTE(NULL); +-------------+ | QUOTE(NULL) | +-------------+ | NULL +-------------+ 1 row in set (0.00 sec) mysql> Select Name, QUOTE(NULL) from student where id = 1; +--------+-------------+ | Name | QUOTE(NULL) | +--------+-------------+ | Gaurav | NULL | +--------+-------------+ 1 row in set (0.08 sec)
