Question

我有一个名为associate_ratings的表，其结构如下：

id  int(11) NO  PRI     auto_increment
associate   varchar(10) NO          
skill_id    int(11) NO  MUL             
rating  int(11) NO          
updated_time    datetime    NO

此表格包含该员工的技能（skill_id）及其相应的rating。评级栏可以取值（1,2,3）我想获得每项技能中有多少员工获得特定评级，请在下面输出表结构中找到：

Skill_id  Rating1_count Rating2_count  Rating3_count

Java        2             1               4
C#          3             2               2

这在Java中表示有2个评级为1,1的同事评级为2＆amp; 4名员工评级为3

我尝试了以下查询，但输出的格式不符合我的预期：

SELECT skill_id, rating, count(*) FROM associate_ratings a
WHERE updated_time = (
   SELECT max(updated_time)
   FROM skill_set.associate_ratings b
   WHERE a.associate = b.associate
) GROUP BY a.skill_id, a.rating order by a.skill_id, a.rating;

您能告诉我如何以我想要的格式获取输出吗？

Answer 1

使用临时表和案例

SELECT  skill_id, sum(rating_1), sum(rating_2), sum(rating_3)
    FROM (
     SELECT a.skill_id as skill_id, 
            case a.rating when '1' then 1  else 0 end  as rating_1,
            case a.rating when '2' then 1  else 0 end  as rating_2,           
            case a.rating when '3' then 1  else 0 end  as rating_3
    FROM associate_ratings a
    WHERE updated_time = (
       SELECT max(updated_time)
       FROM skill_set.associate_ratings b
       WHERE a.associate = b.associate
    ) ) as t
 GROUP BY skill_id
 ORDER BY skill_id;

Answer 2

select Skill_id  , 
  count(case when rating = 1 then 1 else null end) as Rating1_count ,
  count(case when rating = 2 then 1 else null end) as Rating2_count ,
  count(case when rating = 3 then 1 else null end) as Rating3_count 
from associate_ratings  b
left join associate_ratings  a
  on b.Skill_id = a.Skill_id
group by Skill_id

Answer 3

这将是这样的：

SELECT 
    skill_id, 
    sum(IF(rating=1,1,0)) as Rating1_count, 
    sum(IF(rating=2,1,0)) as Rating2_count, 
    sum(IF(rating=3,1,0)) as Rating3_count
FROM associate_ratings 
GROUP BY skill_id
ORDER BY skill_id;

我认为这是最简单的解决方案。

如何显示每个评级的员工数量？

3 个答案: