SQL复杂查询

Question

编辑：

我的表由 id、segmentID、月、年和平均速度组成，我在这里创建了一些演示数据的 sqlfiddle： http ://sqlfiddle.com/#!2/183c1/1

我需要识别上个月平均行驶速度下降超过 10% 的路段。

有人可以帮我吗？ 谢谢

谢谢

Answer 1

您需要选择每个月，加入下个月（由于您的表结构，这有点令人费解）并找到减少（/增加）。 尝试以下复杂查询

SELECT 
   t1.segmentID, t1.month, t1.year, AVG(t1.avgSpeed) as avgSpeed1, 
   AVG(t2.avgSpeed) as avgSpeed2,
   1-(AVG(t1.avgSpeed)/AVG(t2.avgSpeed)) as decrease
FROM 
   travels t1
LEFT JOIN 
   travels t2
ON 
   CONCAT(t2.year,'-',LPAD(t2.month,2,'00'),'-',LPAD(1,2,'00')) = DATE_ADD(CONCAT(t1.year,'-',LPAD(t1.month,2,'00'),'-',LPAD(1,2,'00')), INTERVAL -1 MONTH)
GROUP BY 
   segmentID, month, year
HAVING 
   avgSpeed1/avgSpeed2 < .9

这是更新的 SQLFiddle - http://sqlfiddle.com/#!2/183c1/25

Answer 2

这是我的解决方案

Sqlfidle 演示

关键是要跟踪上个月和下个月之间的关系，所以我正在做 year*100+month 和 after group by year and moth 检查 year*100+month 字段中的差异 1 和 89。 同样遗憾的是，MySQL 不支持 CTE，并且使用派生表使查询变得丑陋。

代码：

select s.month,s.speed,m.month as prevmonth,m.speed as sp, 100-s.speed/m.speed*100 as speeddiff  from
(SELECT segmentid,month,year*100+month as mark,avg(avgSpeed) as speed from travels
group by segmentid,month,year*100+month
) as s
,
(SELECT segmentid,month,year*100+month as mark,avg(avgSpeed) as speed from travels
group by segmentid,month,year*100+month
) as m   
where s.segmentid=m.segmentid and (s.mark=m.mark+1 or s.mark=m.mark+89) and (m.speed-(m.speed/10))>s.speed;

CTE 代码适用于除 MySQL 之外的每个数据库

with t  as(SELECT segmentid,month,year*100+month as mark,avg(avgSpeed) as speed from travels
group by segmentid,month,year*100+month
)
select s.month,s.speed,m.month as prevmonth,m.speed as sp, 100-s.speed/m.speed*100 as speeddiff from t s 
inner join t m on s.segmentid=m.segmentid and (s.mark=m.mark+1 or s.mark=m.mark+89)
where (m.speed-(m.speed/10))>s.speed;

Answer 3

这需要自联接。 这个答案会让你开始。 你可以处理细节。

select somefields
from yourtable t1 join yourtable t2 on t1.something = t2.something
where t1.month = whatever
and t2.month = t1.month + 1
and t2.speed <= t1.speed * .9