MySQL查询:限制加入

Question

说我有两张桌子想加入.分类:

id   name
----------
1    Cars
2    Games
3    Pencils

和项目:

id   categoryid   itemname
---------------------------
1    1            Ford
2    1            BMW
3    1            VW
4    2            Tetris
5    2            Pong
6    3            Foobar Pencil Factory

我想要一个返回类别和第一个(也是唯一的)itemname的查询:

category.id category.name item.id item.itemname
-------------------------------------------------
1           Cars          1       Ford
2           Games         4       Tetris
3           Pencils       6       Foobar Pencil Factory

有没有办法可以获得随机结果:

category.id category.name item.id item.itemname
-------------------------------------------------
1           Cars          3       VW
2           Games         5       Pong
3           Pencils       6       Foobar Pencil Factory

谢谢!

Answer 1

刚做了一个快速测试.这似乎有效:

mysql> select * from categories c, items i
    -> where i.categoryid = c.id
    -> group by c.id;
+------+---------+------+------------+----------------+
| id   | name    | id   | categoryid | name           |
+------+---------+------+------------+----------------+
|    1 | Cars    |    1 |          1 | Ford           |
|    2 | Games   |    4 |          2 | Tetris         |
|    3 | Pencils |    6 |          3 | Pencil Factory |
+------+---------+------+------------+----------------+
3 rows in set (0.00 sec)

我认为这将满足你的第一个问题.不确定第二个 - 我认为需要一个内部查询与random()或类似的东西!