Question

我想从表中选择唯一的一行，有人可以帮帮我吗？

 SELECT * FROM table
 where to_user = ? 
 and deleted != ? 
 and del2 != ?
 and is_read = '0' 
  order by id desc


+----+-----+------+
| id | message_id |
+----+-----+------+
|  1 | 23         | 
|  2 | 23         | 
|  3 | 23         | 
|  4 | 24         | 
|  5 | 25         | 
+----+-----+------+

我需要像

这样的东西

+----+-----+------+
| id | message_id |
+----+-----+------+
|  3 | 23         | 
|  4 | 24         | 
|  5 | 25         | 
+----+-----+------+

Answer 1

试试这个：

SELECT MAX(id), message_id
FROM tablename
GROUP BY message_id

如果您还有其他字段：

SELECT MAX(id), message_id
FROM tablename
WHERE to_user = ? 
AND deleted != ? 
AND del2 != ?
AND is_read = '0'
GROUP BY message_id 
ORDER BY id DESC

Answer 2

如果您只需要特定message_id的最大ID

SELECT max(id), message_id FROM table
 where to_user = ? 
 and deleted != ? 
 and del2 != ?
 and is_read = '0'
group by message_id 
  order by id desc

Answer 3

尝试使用DISTINCT关键字。这肯定会有效：

SELECT DISTINCT(message_id), id FROM table;

mysql只选择唯一的行

3 个答案: