我有一个日志表,我想在其中选择特定记录组的条目,这些记录按我不知道的ID分组。 参见下表,还有更多列,但这些列与问题无关。
-------------------------------------------------------
| id | details | deviceId | processId | timestamp |
-------------------------------------------------------
| 1 | startup | 753 | 538 | 1546346190 |
| 2 | processing | 753 | 538 | 1546346192 |
| 3 | logging | 753 | 538 | 1546346217 |
| 4 | done | 753 | 538 | 1546346220 |
| 5 | startup | 567 | 539 | 1590648690 |
| 6 | processing | 567 | 539 | 1590648692 |
| 7 | logging | 567 | 539 | 1590648717 |
| 8 | done | 567 | 539 | 1590648720 |
| 9 | startup | 753 | 540 | 1590655888 |
| 10 | processing | 753 | 540 | 1590655890 |
| 11 | logging | 753 | 540 | 1590655915 |
| 12 | email sent | 753 | 540 | 1590655918 |
| 13 | done | 753 | 540 | 1590655920 |
-------------------------------------------------------
我想获取一个设备的一个进程的最后一个条目 当我查询这样的信息时,我会获得设备的所有记录:
SELECT *
FROM logtable
WHERE deviceId = 753
ORDER BY timestamp DESC
当我不知道进程ID为540时,如何只在一个查询中获得带有进程ID 540的记录?
我已经用子查询尝试过了:
SELECT *
FROM logtable
WHERE processId IN (
SELECT processId
FROM logtable
WHERE deviceId = 753
ORDER BY timestamp DESC
LIMIT 1
)
But MariaDB doesn't accept LIMIT
in a subquery
Use
=
:You only need
IN
if the subquery is going to return multiple rows.