左连接查询

左连接查询语句表1 left join 表2 on 条件； 然后where，having，group等语句可以照常使用以下例子用两次左连接进行匹配select t1.tname,mres,t2.tname,matime from m left join t as t1 on t1.tid=m.hid left join t as t2 on t2.tid=m.gid;

mysql> set names gbk;Query OK, 0 rows affected (0.02 sec)mysql> use qq;Database changedmysql> create table m(-> mid int not null primary key,-> hid int ,-> gid int ,-> mres varchar(20),-> matime date-> )engine myisam charset utf8;Query OK, 0 rows affected (0.11 sec)mysql> mysql> create table t(-> tid int ,-> tname varchar(20)-> )engine myisam charset utf8;Query OK, 0 rows affected (0.03 sec)mysql> mysql> insert into m-> values-> (1,1,2,'2:0','2006-05-21'),-> (2,2,3,'1:2','2006-06-21'),-> (3,3,1,'2:5','2006-05-25'),-> (4,2,1,'3:2','2006-07-21');Query OK, 4 rows affected (0.00 sec)Records: 4  Duplicates: 0  Waings: 0mysql> insert into t-> values-> (1,'国安'),-> (2,'申花'),-> (3,'公益联队');Query OK, 3 rows affected (0.02 sec)Records: 3  Duplicates: 0  Waings: 0mysql> select $ from m;ERROR 1054 (42S22): Unknown column '$' in 'field list'mysql> select * from m;+-----+------+------+------+------------+| mid | hid  | gid  | mres | matime |+-----+------+------+------+------------+|1 |1 |2 | 2:0  | 2006-05-21 ||2 |2 |3 | 1:2  | 2006-06-21 ||3 |3 |1 | 2:5  | 2006-05-25 ||4 |2 |1 | 3:2  | 2006-07-21 |+-----+------+------+------+------------+4 rows in set (0.03 sec)mysql> #将所有队列序号改为名字mysql> select t1.tname,mres,t2.tname,matime from-> m left join t as t1 on t1.tid=m.hid-> left join t as t2 on t2.tid=m.gid;+----------+------+----------+------------+| tname| mres | tname| matime |+----------+------+----------+------------+| 国安 | 2:0  | 申花| 2006-05-21 || 申花| 1:2  | 公益联队 | 2006-06-21 || 公益联队 | 2:5  | 国安 | 2006-05-25 || 申花| 3:2  | 国安 | 2006-07-21 |+----------+------+----------+------------+4 rows in set (0.01 sec)