Question

根据机器ID列（＆＃39; mid＆＃39;），我有两个MYSQL表，我这是一个LEFT JOIN。

机＆＃39;表

+-----+-------------+-------------+-----+---------------------+
| mid | machineName |  ipAddress  | nid |      modified       |
+-----+-------------+-------------+-----+---------------------+
|   1 | machine1    | 192.168.1.1 |  16 | 2018-01-28 19:48:53 |
|   2 | machine2    | 192.168.2.1 |  16 | 2018-01-29 16:28:11 |
+-----+-------------+-------------+-----+---------------------+

＆＃39; user_reverts＆＃39;表

+----+-----+-----+---------------------+
| id | uid | mid |      modified       |
+----+-----+-----+---------------------+
| 11 | 189 |  1  | 2018-01-30 10:01:10 |
| 13 | 189 |  2  | 2018-01-30 12:11:50 |
| 14 | 190 |  1  | 2018-01-26 17:09:17 |
| 15 | 190 |  2  | 2018-01-25 15:51:31 |
| 16 | 189 |  2  | 2018-01-30 19:48:58 |
+----+-----+-----+---------------------+

查询计算自每天开始以来用户在每台计算机上进行的还原次数，并按机器对其进行分组。

SELECT machines.mid as mid, machines.machineName as machineName,
        machines.ipAddress as ipAddress, coalesce(reverts.count, 0) as count, 
        coalesce(reverts.modified,'never') as reverted FROM
            (SELECT mid, machineName, INET6_NTOA(ipAddress) as ipAddress FROM machines) machines
            LEFT JOIN
            (SELECT machines.mid,user_reverts.modified,count(*) as count FROM machines
            INNER JOIN user_reverts ON user_reverts.mid=machines.mid AND user_reverts.uid = 189
            WHERE DATE(user_reverts.modified) = CURDATE() group by user_reverts.mid) reverts 
            ON reverts.mid = machines.mid

它运作良好，但我希望“恢复”＆＃39;列显示最新的时间和日期，因此预期的结果将是

+-----+-------------+-------------+-------+---------------------+
| mid | machineName |  ipAddress  | count |      reverted       |
+-----+-------------+-------------+-------+---------------------+
|   1 | machine1    | 192.168.1.1 |     1 | 2018-01-24 10:01:10 |
|   2 | machine2    | 192.168.2.1 |     2 | 2018-01-30 19:48:58 | (latest)
+-----+-------------+-------------+-------+---------------------+

我试图替换

coalesce(reverts.count, 0)

与

MAX(reverts.count, 0)

但我收到一条错误消息。我该怎么做？感谢

Answer 1

您可以添加其他列并简化查询：

        SELECT machines.mid as mid
         , machines.machineName as machineName
         , INET6_NTOA(ipAddress) as ipAddress
         , coalesce(count(*), 0) as count 
         , coalesce(MAX(user_reverts.modified),'never') as reverted  -- latest revert 
      FROM machines
 LEFT JOIN user_reverts
        ON ( user_reverts.mid=machines.mid AND user_reverts.uid = 189 )
     WHERE DATE(user_reverts.modified) = CURDATE()
  GROUP BY machines.mid
         ;

查看this SQLFiddle（当然，确切的表格定义可能与您的不同）。

如何在MYSQL LEFT JOIN

1 个答案: