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!!