sql - Oracle:如何使 "group by"超过一个范围？

Question

如果我有一个这样的表:

pkey   age
----   ---
   1     8
   2     5
   3    12
   4    12
   5    22

我可以“分组”来计算每个年龄。

select age,count(*) n from tbl group by age;
age  n
---  -
  5  1
  8  1
 12  2
 22  1

我可以使用什么查询来按年龄范围进行分组？

  age  n
-----  -
 1-10  2
11-20  2
20+    1

我使用 10gR2，但我也对任何特定于 11g 的方法感兴趣。

Answer 1

SELECT CASE 
         WHEN age <= 10 THEN '1-10' 
         WHEN age <= 20 THEN '11-20' 
         ELSE '21+' 
       END AS age, 
       COUNT(*) AS n
FROM age
GROUP BY CASE 
           WHEN age <= 10 THEN '1-10' 
           WHEN age <= 20 THEN '11-20' 
           ELSE '21+' 
         END