如何在一個SQL查詢中多次使用where條件

Question

在我的table1有這樣的日期：

id      value
1       500
2       400
3       300
4       200
5       100

我想在show表中設置以上數據：

d1      d2      d3      d4      d5
500     400     300     200     100

我正在使用以下sql查詢。

"SELECT `value` as d1 from `table1` WHERE `id`=1"
"SELECT `value` as d2 from `table1` WHERE `id`=2"
"SELECT `value` as d3 from `table1` WHERE `id`=3"
"SELECT `value` as d4 from `table1` WHERE `id`=4"
"SELECT `value` as d5 from `table1` WHERE `id`=5"   

如何在單個sql查詢中進行所有查詢？

Answer 1

我將使用聚合：

select max(case when id = 1 then value end) as d1,
       max(case when id = 2 then value end) as d2,
       max(case when id = 3 then value end) as d3,
       max(case when id = 4 then value end) as d4,
       max(case when id = 5 then value end) as d5
from t;

Answer 2

如果可以使用單獨的行，則只需過濾值即可：

select id, 
    value 
from t
where id in (1,2,3,4,5);

如果在單個行中需要所有值，請使用where過濾所有行，並使用條件聚合來透視數據：

select max(case when id = 1 then value end) as d1,
       max(case when id = 2 then value end) as d2,
       max(case when id = 3 then value end) as d3,
       max(case when id = 4 then value end) as d4,
       max(case when id = 5 then value end) as d5
from t
where id in (1,2,3,4,5);