如何在 SQL 中使用数据透视表？

Question

我有一个 table 如下所示：

需要将其转换成以下格式：

数据为A、B、C级别。尝试使用 case when 如下所示，但它会导致多行。所以想用一个pivot。

Select a,b,c,
       case when D = N and E = 1 then N1 = value,
       case when D = N and E = 2 then N2 = value,
       case when D = O and E = 1 then O1 = value,
       case when D = O and E = 2 then O2 = value,

如有任何帮助，我们将不胜感激。谢谢！

Answer 1

使用聚合：

Select a, b, c,
       max(case when D = 'N' and E = 1 then value end) as N1,
       max(case when D = 'N' and E = 2 then value end) as N2,
       max(case when D = 'O' and E = 1 then value end) as O1,
       max(case when D = 'O' and E = 2 then value end) as O2
from t
group by a, b, c;

请注意，这也修复了 case 表达式中的逻辑。