-- 创建数据表create table score(id int not null auto_increment,score int not null,primary key (id))engine=myisam;-- 插入数据insert into score(`score`) values(100),(200),(200),(100),(300),(400),(500),(300),(200),(400),(500),(200),(500),(300);-- 范围分组SELECT count(a.score_class),a.score_classFROM    (SELECT         id,            score,            (CASE                WHEN score >= 100 AND score <= 200 THEN 1                WHEN score > 200 AND score <= 300 THEN 2                WHEN score > 300 AND score <= 400 THEN 3                WHEN score > 400 AND score <= 500 THEN 4                ELSE 5            END) AS score_class    FROM        score) AS a   group by a.score_class;-- output +----------------------+-------------+| count(a.score_class) | score_class |+----------------------+-------------+|                    7 |           1 ||                    3 |           2 ||                    2 |           3 ||                    3 |           4 |+----------------------+-------------+4 rows in set (0.00 sec)-- indexmysql> show index from score;+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| score |          0 | PRIMARY  |            1 | id          | A         |          15 |     NULL | NULL   |      | BTREE      |         |               |+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+1 row in set (0.00 sec)-- explain+----+-------------+------------+------+---------------+------+---------+------+------+---------------------------------+| id | select_type | table      | type | possible_keys | key  | key_len | ref  | rows | Extra                           |+----+-------------+------------+------+---------------+------+---------+------+------+---------------------------------+|  1 | PRIMARY     | 
    
      | ALL  | NULL          | NULL | NULL    | NULL |   15 | Using temporary; Using filesort ||  2 | DERIVED     | score      | ALL  | NULL          | NULL | NULL    | NULL |   15 | NULL                            |+----+-------------+------------+------+---------------+------+---------+------+------+---------------------------------+2 rows in set (0.04 sec)-- 写在最后, 这篇文章和上一篇文章是有关系的, -- 区别点:-- 1  分组求和的方式不同-- 2  有一个行转列的过程.