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!!

主表如何统计在附表中的出现次数？