先建立一张 m 表
mysql> create table m ( -> mid int, -> hid int, -> gid int, -> mres varchar(10), -> matime date -> )engine myisam charset utf8; Query OK, 0 rows affected (0.07 sec)
mysql> insert into m
-> values
-> (1, 1, 2, '2:0', '2018-08-03'),
-> (2, 2, 3, '1:2', '2018-08-03'),
-> (3, 3, 1, '2:5', '2018-08-04'),
-> (4, 2, 1, '3:2', '2018-08-05');
Query OK, 4 rows affected (0.00 sec)
再建立一个 t 表
mysql> create table t( -> tid int, -> tname varchar(10) -> )engine myisam charset utf8; Query OK, 0 rows affected (0.07 sec)
mysql> insert into t
-> values
-> (1, '甲'),
-> (2, '乙'),
-> (3, '丙');
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
题目要求:把hid和gid中的数字替换成tid中的tname
(一)根据m表和t表左连接,把hid替换成t表的tname
(二)把(一)的结果集当成一张表再做一次左连接
把gid替换成t表的tname
或左连接两张表(用两次left join)
union
查出价格低于100元或价格高于4000元的商品
or
或者用union