主表如何统计在附表中的出现次数？

主表如何统计在附表中的出现次数？

建立主表：

create table a1 (id int ,name char(20));

建立附表:

create table a2 (tid int ,name char(20));

分别插入数据:

mysql> insert into a1 values (1,'baidu');Query OK, 1 row affected (0.00 sec)mysql> insert into a1 values (2,'qq');Query OK, 1 row affected (0.00 sec)mysql> insert into a1 values (3,'sina');Query OK, 1 row affected (0.02 sec)mysql> insert into a2 values (1,'000');Query OK, 1 row affected (0.00 sec)mysql> insert into a2 values (1,'001');Query OK, 1 row affected (0.00 sec)mysql> insert into a2 values (1,'002');Query OK, 1 row affected (0.00 sec)mysql> insert into a2 values (1,'003');Query OK, 1 row affected (0.00 sec)mysql> insert into a2 values (2,'200');Query OK, 1 row affected (0.00 sec)mysql> insert into a2 values (2,'201');Query OK, 1 row affected (0.00 sec)mysql> insert into a2 values (2,'202');Query OK, 1 row affected (0.00 sec)mysql> insert into a2 values (2,'203');Query OK, 1 row affected (0.00 sec)mysql> insert into a2 values (2,'204');Query OK, 1 row affected (0.00 sec)mysql> insert into a2 values (2,'205');Query OK, 1 row affected (0.01 sec)mysql> insert into a2 values (3,'300');Query OK, 1 row affected (0.01 sec)

sql语句：

select a.*,(select count(1) from a2 as b where b.tid=a.id) from a1 as a;

这样就能查询a1中所有的id，对应的在a2表中出现了多少次!!

posted on2014-07-12 22:42一生学习,何来毕业阅读(...) 评论(...)编辑

博客园首页博问新闻闪存程序员招聘知识库