mysql 统计

create table u(
id int,
name varchar(8),
age int
);


mysql> select * from u;
+------+--------+------+
| id   | name   | age  |
+------+--------+------+
|    1 | tonny  |   18 |
|    1 | wendy  |   30 |
|    1 | james  |   25 |
|    1 | simon  |   22 |
|    1 | flynn  |   35 |
|    1 | nancy  |   42 |
|    1 | olivia |   51 |
|    1 | linda  |   20 |
+------+--------+------+
8 rows in set (0.00 sec)

 

要求得到效果如下：
统计出不同年龄段的人数：

  年龄段 人数  
  18-20 2  
  21-30 3  
  31-40 1  
  41-50 1  
  > 50 1   

 

 

mysql> select elt(interval(age,18,21,31,41,51),
    ->  '18-20',
    ->  '21-30',
    ->  '31-40',
    ->  '41-50',
    ->  '> 50'
    -> ) as `年龄段`
    -> ,count(*) as `人数`
    -> from u
    -> group by elt(interval(age,18,21,31,41,51),
    ->  '18-20',
    ->  '21-30',
    ->  '31-40',
    ->  '41-50',
    ->  '> 50'
    -> );
+--------+------+
| 年龄段 | 人数 |
+--------+------+
| 18-20  |    2 |
| 21-30  |    3 |
| 31-40  |    1 |
| 41-50  |    1 |
| > 50   |    1 |
+--------+------+
5 rows in set (0.03 sec)

mysql>