SQL從所有選定行減去第一行

Question

有沒有辦法從所有行中減去第一個選定行的值？所以，如果我有

t = 1, v = 500 
t = 2, v = 800 
t = 3, v = 1200 

我會得到

t = 1, v = 0 
t = 2, v = 300 
t = 3, v = 700 

我一直在尋找一種便攜式解決方案，但一個Postgres的解決方案可以使用原來的:-) 謝謝。

Answer 1

SELECT v - FIRST_VALUE(v) OVER (ORDER BY t) 
FROM mytable 
ORDER BY 
     t 

Answer 2

像這樣的東西可能工作

SELECT mt2.t, mt2.v - mt1.v AS v 
FROM MyTable mt1 
CROSS JOIN MyTable mt2 
WHERE mt1.t = 1 

Answer 3

大多數便攜式的方式，而無需使用窗口功能：

select v - first 
from 
    mytable, 
    (select v as first from mytable order by t limit 1) as inner 
order by t