查询获取MAX值和对应的日期

Question

Table

+---------------------+-----------------------------+--------------+----------+
| timestamp           | hostname                    | LICENSECOUNT | MAX_USED |
+---------------------+-----------------------------+--------------+----------+
| 2021-02-03 17:00:03 | server1                     |          125 |      10  |
| 2021-02-03 17:00:06 | server2                     |          415 |      50  |
| 2021-02-26 18:00:07 | server1                     |          125 |      125 |
| 2021-02-26 18:00:09 | server2                     |          415 |      415 |
| 2021-03-05 17:00:02 | server1                     |          125 |      115 |
| 2021-03-05 17:00:04 | server2                     |          415 |      315 |

My query - Get the max value for license count grouped by server in the past 30 days

select 
    timestamp, hostname, LICENSECOUNT, max(currentused) as MAX_USED 
from 
    LICENSECHECKS 
where 
    TIMESTAMP BETWEEN DATE_SUB(NOW(), INTERVAL 30 DAY) AND NOW() 
group by hostname;

My result - The timestamp is the start of the dataset (30 days ago)

+---------------------+-----------------------------+--------------+----------+
| timestamp           | hostname                    | LICENSECOUNT | MAX_USED |
+---------------------+-----------------------------+--------------+----------+
| 2021-02-03 17:00:03 | server1                     |          125 |      125 |
| 2021-02-03 17:00:06 | server2                     |          415 |      415 |

My Desired Result - The timestamps are corresponding to the dates which

+---------------------+-----------------------------+--------------+----------+
| timestamp           | hostname                    | LICENSECOUNT | MAX_USED |
+---------------------+-----------------------------+--------------+----------+
| 2021-02-26 18:00:07 | server1                     |          125 |      125 |
| 2021-02-26 18:00:09 | server2                     |          415 |      415 |

Answer 1

In a sub-query select statement add the following

 ROW_NUMBER() OVER (PARTITION BY hostname ORDER BY currentuserid DESC) as RN

Then pull the row(s) with RN = 1 in the outer query where statement

Answer 2

You can use:

select lc.*
    timestamp, hostname, LICENSECOUNT, max(currentused) as MAX_USED 
from LICENSECHECKS 
where lc.currentused = (select max(lc2.currentused)
                        from licensechecks lc2
                        where lc2.timestamp >= now() - interval 30 day and
                              lc2.hostname = lc.hostname
                       );

Notes:

• This assumes no future timestamps .
• This will return duplicates if there are duplicate max values (which can be handled with a tweak).
• now() has a time component. I suspect that you might want something like curdate() - interval 29 day .