加入职位

Question

我有表baskets,fruits和basket_fruits(join-table :) basket_id-fruit_id.

我怎样才能在篮子里找回每个水果的位置,这样我就会得到类似的东西

+---------------------------------------+
| basket_id | fruit_id | fruit_position |
|---------------------------------------|
| 1         | 2        | 1              |
| 1         | 5        | 2              |
+---------------------------------------+

果实位置只是返回的连接表中的一行(它不是列).

Schema:
baskets:       id, title
fruits:        id, title
basket_fruits: id, basket_id, fruit_id

Answer 1

MySQL 不支持测距函数,因此您必须使用子查询:

SELECT  basket_id, fruit_id,
        (
        SELECT  COUNT(*)
        FROM    basket_fruit bfi
        WHERE   bfi.basket_id = bf.basket_id
                AND bfi.fruit_id <= bf.fruit_id
        ) AS fruit_position
FROM    basket_fruit bf
WHERE   basket_id = 1

或使用会话变量(更快但依赖于未记录的实现细节,可能在将来的版本中中断):

SET @rn = 0;

SELECT  basket_id, fruit_id, @rn := @rn + 1 AS fruit_position
FROM    basket_fruit bf
WHERE   basket_id = 1
ORDER BY
        fruit_id