首先执行如下操作：

mysql> create table main(id integer unsigned);

mysql> create table test1(id integer unsigned,body text);
Query OK, 0 rows affected (0.84 sec)

mysql> insert into main(id) value(1);
Query OK, 1 row affected (0.16 sec)

mysql> insert into test1(id,body) value(1,'something1');
Query OK, 1 row affected (0.27 sec)

mysql> insert into test1(id,body) value(1,'something2');
Query OK, 1 row affected (0.00 sec)

再执行：

mysql> select main.id,body from main
    -> left join test1 on main.id=test1.id
    -> group by main.id;

得到：

+------+------------+
| id   | body       |
+------+------------+
|    1 | something1 |
+------+------------+
1 row in set (0.02 sec)

如何从test1表中得到这个呢？

+------+------------+
| id   | body       |
+------+------------+
|    1 | something1 something2  |
+------+------------+
1 row in set (0.02 sec)