postgres加入同一張桌子

Question

我有一張看起來像這樣的桌子

years  type     value    x      y
1      b        3.74637  false  true
1      b        -0.52816 true   false
1      mon1     0        true   false
1      mon1     0        false  true
1      mon10    0.00413  true   false
1      mon10    0.00137  false  true

我希望桌子看起來像

years  type     x        y
1      b        3.74637  -0.52816
1      mon1     0        0
1      mon10    0.00413  0.00137

因此，我創建了一個請求，在該請求上我自己連接了表

SELECT 
     i.years, 
     i.type, 
     i.value as b, 
     j.value as m 
from abc as i 
inner join abc as j on i.type = j.type AND i.years = j.years 
WHERE i.type = j.type AND i.m = j.b 

現在我明白了

years   type    x        y
1       b       3.74637  -0.52816
1       b       -0.52816 3.74637
1       mon1    0        0
1       mon1    0        0
1       mon10   0.00413  0.00137
1       mon10   0.00137  0.00413

我如何擺脫線的x值等於下一行的y的雙峰

Answer 1

您可以使用聚合：

Select years, type,
   Max (case when x then value end)as x,
   Max (case when y then value end)as y
From t
Group by years, type

Answer 2

假設x和y是真實的布爾列：

select xv.years, xv.type, xv.value as x, yv.value as y
from abc xv
   join abc yv on (xv.years, xv.type) = (yv.years, yv.type) and yv.y
where xv.x;

在線示例： http : //rextester.com/TUQPQH27415

Answer 3

您無需執行任何其他操作，只需在聯接上添加一些其他約束即可。 您確實不希望執行子查詢，因為毫無原因會導致性能下降。

 SELECT 
   i.years, 
   i.type, 
   i.value as b, 
   j.value as m 
 from abc i
 inner join abc j on i.type = j.type and i.x = true and j.y = true;

Answer 4

子查詢：

select x1.*, y2.y
from 
(
    select years, type, value as x
    from MyTable
    where x = 'true'
) x1
left join
(
    select years, type, value as y
    from MyTable
    where y = 'true'
) y2
on x1.years = y2.years
and x1.type = y2.type