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!!