[英]How do I select rows with MAX(datetime) and also get min values for a column?
My table is like this (np_capacity): 我的表是这样的(np_capacity):
id tower datetime capacity
---|----|---------------------|----------
1 | A | 2016-05-29 09:02:41 | 34676
2 | B | 2016-05-29 09:02:41 | 10736
5 | C | 2016-05-29 09:02:41 | 55664
3 | D | 2016-05-29 09:02:41 | 32622
4 | A | 2016-05-29 13:08:38 | 5474
6 | B | 2016-05-29 13:08:38 | 20692
7 | C | 2016-05-29 13:08:38 | 134802
8 | D | 2016-05-29 13:08:38 | 4754
I want to select all the tower with the max date then for those towers I also want the min capacity value in the table. 我想选择所有具有最大日期的塔,然后为这些塔选择表中的最小容量值。
Result would be: 结果将是:
id tower datetime capacity MinCapacity
---|----|---------------------|----------|-------------
4 | A | 2016-05-29 13:08:38 | 5474 | 5474
6 | B | 2016-05-29 13:08:38 | 20692 | 10736
7 | C | 2016-05-29 13:08:38 | 134802 | 55664
8 | D | 2016-05-29 13:08:38 | 4754 | 4754
What I have is this but it doesnt always give my the correct min values. 我所拥有的是这个,但它并不总是能给出正确的最小值。
SELECT npc.*, groupedcap.MinCapacity
FROM np_capacity npc
INNER JOIN
(SELECT tower, MAX(date) AS MaxDate
FROM np_capacity
GROUP BY tower) groupednpc
ON npc.tower = groupednpc.tower
INNER JOIN
(SELECT tower, MIN(capacity) AS MinCapacity
FROM np_capacity
GROUP BY tower) groupedcap
ON npc.tower = groupedcap.tower
AND npc.date = groupednpc.MaxDate
You can use a subselect to calculate the min capacity, and the max date. 您可以使用子选择来计算最小容量和最大日期。 Then, join with the table to get other fields. 然后,与表联接以获取其他字段。
select npc.*, calc.minCapacity
from (
select tower, max(datetime) maxDate, min(capacity) minCapacity
from np_capacity
group by tower
) calc
join np_capacity npc on (npc.tower = calc.tower
and npc.datetime = npc.maxDate)
This request select all towers, and for each the maxdatetime and mincapacity. 该请求选择所有塔,并选择每个塔的最大日期时间和最小容量。
If you want just the towers with the maxdatetime, you can use : 如果只需要具有maxdatetime的塔,则可以使用:
select npc.*, (select min(c2.capacity) from np_capacity c2
where c2.tower = npc.tower) minCapacity
from (select max(datetime) maxDatetime from np_capacity) c1
join np_capacity npc on (npc.datetime = c1.maxDatetime)
SELECT `a`.`id`,`a`.`tower`,`a`.`datetime`,`a`.`capacity`,(SELECT MIN(`b`.`capacity`)
FROM `np_capacity` `b` WHERE `b`.`tower`=`a`.`tower` ) AS `MinCapacity` FROM `np_capacity` `a`
WHERE `a`.`datetime`=(SELECT MAX(`datetime`) FROM `np_capacity`);
Test the above query on SQL Fiddle 在SQL Fiddle上测试以上查询
Another answer is by using order by and limit 1 in sub query : 另一个答案是在子查询中使用order by和limit 1:
select t1.*,(select capacity from np_capacity t3
where t1.tower=t3.tower
order by capacity limit 1) mincapacity
from np_capacity t1 where
datetime=(select datetime from np_capacity
order by datetime desc limit 1);
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.