SQL復雜查詢

Question

編輯：

我的表由 id、segmentID、月、年和平均速度組成，我在這里創建了一些演示數據的 sqlfiddle： http ://sqlfiddle.com/#!2/183c1/1

我需要識別上個月平均行駛速度下降超過 10% 的路段。

有人可以幫我嗎？ 謝謝

謝謝

Answer 1

您需要選擇每個月，加入下個月（由於您的表結構，這有點令人費解）並找到減少（/增加）。 嘗試以下復雜查詢

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

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

Answer 2

這是我的解決方案

Sqlfidle 演示

關鍵是要跟蹤上個月和下個月之間的關系，所以我正在做 year*100+month 和 after group by year and moth 檢查 year*100+month 字段中的差異 1 和 89。 同樣遺憾的是，MySQL 不支持 CTE，並且使用派生表使查詢變得丑陋。

代碼：

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 代碼適用於除 MySQL 之外的每個數據庫

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

這需要自聯接。 這個答案會讓你開始。 你可以處理細節。

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