Mysql 按最后一个未知id获取一组记录
我有一个日志表,我想在其中选择一组特定记录的条目,这些记录按我不知道的id分组。Mysql 按最后一个未知id获取一组记录,mysql,sql,mariadb,Mysql,Sql,Mariadb,我有一个日志表,我想在其中选择一组特定记录的条目,这些记录按我不知道的id分组。 见下表,有更多列,但这些列与问题无关 ------------------------------------------------------- | id | details | deviceId | processId | timestamp | ------------------------------------------------------- | 1 | startup | 75
见下表,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 |
-------------------------------------------------------
我想为一台设备获取一个进程的最后条目当我查询类似的内容时,我会得到设备的所有记录:
SELECT *
FROM logtable
WHERE deviceId = 753
ORDER BY timestamp DESC
当我不知道processId为540时,如何在一次查询中仅获取processId为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
)
但是MariaDB不接受子查询中的限制使用=
:
SELECT l.*
FROM logtable l
WHERE processId = (SELECT l2.processId
FROM logtable l2
WHERE l2.deviceId = 753
ORDER BY l2.timestamp DESC
LIMIT 1
);
如果子查询要返回多行,则只需在
中输入 顺便说一句,这是这个标签下最常见的问题。标准溶液如下:
SELECT x.*
FROM logtable x
JOIN
( SELECT processId
, MAX(timestamp) timestamp
FROM logtable
WHERE deviceId = 753
GROUP
BY processid
) y
ON y.processid = x.processid
AND y.timestamp = x.timestamp
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