我有一个这样的表:
// requests
+----+----------+-------------+
| id | id_user | unix_time |
+----+----------+-------------+
| 1 | 2353 | 1339412843 |
| 2 | 2353 | 1339412864 |
| 3 | 5462 | 1339412894 |
| 4 | 3422 | 1339412899 |
| 5 | 3422 | 1339412906 |
| 6 | 2353 | 1339412906 |
| 7 | 7785 | 1339412951 |
| 8 | 2353 | 1339413640 |
| 9 | 5462 | 1339413621 |
| 10 | 5462 | 1339414490 |
| 11 | 2353 | 1339414923 |
| 12 | 2353 | 1339419901 |
| 13 | 8007 | 1339424860 |
| 14 | 7785 | 1339424822 |
| 15 | 2353 | 1339424902 |
| 16 | 2353 | 1466272801 |
| 17 | 2353 | 1466272805 |
+----+----------+-------------+
我正在尝试获取与特定用户相关的最后一行。例如对于这个用户 id_user = 7785 我想选择这一行:
| 14 | 7785 | 1339424822 |
这是我的查询:
SELECT unix_time AS last_seen
FROM requests WHERE id = '7785'
ORDER BY unix_time DESC
LIMIT 1
但是我的查询没有选择任何行。怎么了？
SQL fiddle
另请注意，您能否告诉我应该在 id_user 和 uinx_time 上创建单个索引还是应该在这两列上创建多列索引 (id_user, unix_time)?
最佳答案
您使用了错误的列(id 而不是 id_user — 反之亦然):
SELECT unix_time AS last_seen
FROM requests WHERE id_user = '7785'
ORDER BY unix_time DESC
LIMIT 1
关于mysql - 如何为特定用户选择最后一行？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/37993318/