MYSQL-在两列中选择dISTINCT值

Question

我想选择上一次sender_id或receiver_id = 20的地方。

Table:
sender_id   receiver_id     created_time
20            30              1
30            20              2
20            30              3
20            40              4
40            20              5
20            20              6
20            30              7
50            60              9

Result:
sender_id   receiver_id     created_time
40            20              5
20            30              7

Answer 1

像这样：

SELECT LEAST(sender_id, receiver_id), 
       GREATEST(sender_id, receiver_id),
       MAX(created_time)
FROM mytable
WHERE 20 IN (sender_id, receiver_id)
GROUP BY LEAST(sender_id, receiver_id), 
         GREATEST(sender_id, receiver_id)

上面的查询为输入(20, 20, 6) 20，20，6）产生了一条附加记录。 您可以在添加额外的谓词WHERE如果你想排除具有相同的记录条款sender_id和receiver_id 。

Answer 2

试试这个代码：

SELECT * FROM new_table AS t1
WHERE
(sender_id = 20 OR receiver_id = 20)
AND
(t1.created_time >= 
 (SELECT MAX(created_time) FROM new_table WHERE sender_id = t1.sender_id)
)