如何在一个SQL查询中多次使用where条件

Question

在我的table1有这样的日期：

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

我想在show表中设置以上数据：

d1      d2      d3      d4      d5
500     400     300     200     100

我正在使用以下sql查询。

"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"   

如何在单个sql查询中进行所有查询？

Answer 1

我将使用聚合：

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

如果可以使用单独的行，则只需过滤值即可：

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

如果在单个行中需要所有值，请使用where过滤所有行，并使用条件聚合来透视数据：

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);