用于透视数据的SQL查询

Question

我有这种表

+------------------+
| Name Date   Category|
+------------------+
| Test1 1/1/2001   2 |
| Test2 2/1/2001   2 |
| Test3 3/1/2001   2 |
| Foo1  5/4/2011   2 |
| Foo2  6/4/2011   2 |
| Test1  6/4/2011  3 |
+------------------+

我想像这样显示结果：

Category   Test1Date    Foo2Date
-------------------------------
2         1/1/2011      6/4/2001    
3         6/4/2011      NULL

我将如何在SQL中执行此操作？

Answer 1

您可以使用带有CASE表达式的聚合函数将数据行转换为列：

select category,
  max(case when name = 'Test1' then date end) Test1Date,
  max(case when name = 'Foo2' then date end) Foo2Date
from yourtable
group by category;

请参阅SQL Fiddle with Demo