Sql 从联接表中选择两个条目(1:m)
我有一个设备表dev和设备日期表dev_数据。关系1:M 开发表:Sql 从联接表中选择两个条目(1:m),sql,postgresql,join,Sql,Postgresql,Join,我有一个设备表dev和设备日期表dev_数据。关系1:M 开发表: | id |name |status | |-----|-------|-------| | 1 |a |111 | |-----|-------|-------| | 2 |b |123 | |-----|-------|-------| | ....|..... |.... | dev_数据表: |id |dev_id |status |date
| id |name |status |
|-----|-------|-------|
| 1 |a |111 |
|-----|-------|-------|
| 2 |b |123 |
|-----|-------|-------|
| ....|..... |.... |
dev_数据表:
|id |dev_id |status |date |
|---|-------|--------|------------------------|
|1 |1 | 123 |2019-04-16T18:53:07.908Z|
|---|-------|--------|------------------------|
|2 |1 | 120 |2019-04-16T18:54:07.908Z|
|---|-------|--------|------------------------|
|3 |1 | 1207 |2019-04-16T18:55:07.908Z|
|---|-------|--------|------------------------|
|4 |2 | 123 |2019-04-16T18:53:08.908Z|
|---|-------|--------|------------------------|
|5 |2 | 121 |2019-04-16T18:54:08.908Z|
|---|-------|--------|------------------------|
|6 |2 | 127 |2019-04-16T18:55:08.908Z|
|...|.......|........|........................|
我需要选择所有dev并加入dev_数据,但按日期仅添加2条最后记录
最终的响应应该如下所示:
select id, "name", status, max(dd.date) as last,
(select date from device_data p where p.dev_id = device.id and date < dd.date limit 1) as prelast
from device
inner join device_data dd on device.id = dd.dev_id
group by id, "name", status;
select id, "name", status, max(dd.date) as last, max(dd2.date) as prelast,
from device
inner join device_data dd on device.id = dd.dev_id
inner join device_data dd2 on device.id = dd2.dev_id and dd2.date < dd.date
group by id, "name", status;
状态计算1和状态计算2在开发和开发数据中的状态之间存在差异
status_calc_1=>dev_数据和dev的最后一行的状态差异
|id |name |status_calc_1 | status_calc_2 |
|----|------|---------------|---------------|
|1 |a |1207-111 |120-111 |
|----|------|---------------|---------------|
|2 |b |127-123 |121-123 |
status_calc_2=>与dev_数据和dev的上一行的状态差异
|id |name |status_calc_1 | status_calc_2 |
|----|------|---------------|---------------|
|1 |a |1207-111 |120-111 |
|----|------|---------------|---------------|
|2 |b |127-123 |121-123 |
我试过这个:
select id, "name", status, max(dd.date) as last,
(select date from device_data p where p.dev_id = device.id and date < dd.date limit 1) as prelast
from device
inner join device_data dd on device.id = dd.dev_id
group by id, "name", status;
select id, "name", status, max(dd.date) as last, max(dd2.date) as prelast,
from device
inner join device_data dd on device.id = dd.dev_id
inner join device_data dd2 on device.id = dd2.dev_id and dd2.date < dd.date
group by id, "name", status;
还有这个:
select id, "name", status, max(dd.date) as last,
(select date from device_data p where p.dev_id = device.id and date < dd.date limit 1) as prelast
from device
inner join device_data dd on device.id = dd.dev_id
group by id, "name", status;
select id, "name", status, max(dd.date) as last, max(dd2.date) as prelast,
from device
inner join device_data dd on device.id = dd.dev_id
inner join device_data dd2 on device.id = dd2.dev_id and dd2.date < dd.date
group by id, "name", status;
我得到了正确的最后两个dev_数据,但仍然不知道如何创建两列status_calc_1和status_calc_2
status_calc_1=最后一行dev_data.status-dev.status
status\u calc\u 2=上一行dev\u data.status-dev.status您可以使用条件聚合:
select d.id, d.name, d.status,
max(dd.date) as last,
max(case when dd.seqnum = 2 then dd.date end) as prelast,
(max(case when dd.seqnum = 1 then dd.status end) - d.status) as status_calc_1,
(max(case when dd.seqnum = 2 then dd.status end) - d.status) as status_calc_2
from device d join
(select dd.*,
row_number() over (partition by dd.dev_id order by dd.date desc) as seqnum
from device_data dd
) dd
on d.id = dd.dev_id
where seqnum <= 2
group by d.id, d.name, d.status;
我不知道计算结果是什么。您的查询只返回日期。