Question

我有一个名为'items'的表

id      sender  receiver        item
1       1       2               computer
2       2       1               mobile
3       1       3               ipad
4       4       1               ring
5       3       1               camera
6       1       8               pc
7       5       1               ring
8       1       10              tablet

以下查询，如

SELECT receiver id FROM items WHERE sender ='1'
UNION
SELECT sender FROM items WHERE receiver ='1'
ORDER BY 1 DESC

发出订单

如果我想获得发送者/接收者的订单，发送者/接收者的最后一次互动发生在哪里发送者/接收者= 1，我指的是订单（10,5,8,3,4,2）。

在第8行中，user = 1的对手是10

在第7行中，user = 1的对手是5

在第6行，user = 1的对手是8

在第5和第3行，对手用户= 1，是3

在第4行中，user = 1的对手是4

在第1＆amp;第二行，用户= 1的对手是2

Answer 1

尝试这种方式：

SELECT distinct receiver FROM (
SELECT receiver, id FROM items WHERE sender ='1'
UNION
SELECT sender, id FROM items WHERE receiver ='1'
ORDER BY id DESC) sortedtable

10
5
8
3
4
2

Answer 2

或使用分组依据：

SELECT t.user, max(t.id)
FROM
(
  SELECT receiver as user, id FROM items WHERE sender ='1'
  UNION
  SELECT sender as user, id FROM items WHERE receiver ='1'
) as t
GROUP BY t.user
ORDER BY max(t.id) DESC

http://sqlfiddle.com/#!2/5e971/1/0

没有UNION的另一个选项：

SELECT 
  CASE receiver 
    WHEN '1' THEN sender 
    ELSE receiver  
  END as user, 
  max(id) 
FROM items WHERE sender ='1' OR receiver ='1'
GROUP BY user
ORDER BY max(id) DESC

http://sqlfiddle.com/#!2/5e971/3/0

如何根据用户交互对结果进行排序

2 个答案: