case when常见用法分析

目录

case when 语法：

1、case when 条件判断，用于字段

2、case when(+聚合函数+group by实现行转列)

3、分段显示 case when 字段 between ...

---

case when 语法：

case when .. then .. else ..end
注: else 可省略，默认为空。

case when 常用几种用法：

1、case when 条件判断，用于字段

（1）case 字段 when 条件 then 结果1 else 结果2 end

select case deptno when '10' then avg1 else avg2 end from emp;

（2）case when 字段+条件 then 结果1 else 结果2 end

select case when deptno = '10' then avg1 else avg2 end from emp;

2、case when(+聚合函数+group by实现行转列)

select sum(case when deptno=10 then avg1 end)        as bm10
      ,sum(case when deptno=20 then avg1 end)        as bm20 
      ,sum(case when deptno=30 then avg1 end)        as bm30
      ,sum(case when deptno is null then avg1 end)   as bm00
from (select deptno
            ,avg(sal)                                as avg1 
       from emp 
       group by deptno
      );

3、分段显示 case when 字段 between ...

--1.对成绩表中的成绩进行分段,显示[100-85],[85-70],[70-60],[ <60]
select a.*
      ,case when round(score,2) between 85 and 100 then '[100-85]'
            when round(score,2) between 70 and 84.99 then '[85-70]'
            when round(score,2) between 60 and 69.99 then '[70-60]'
            else '[<60]' 
            end  as '分类'
from sc_a01 a
;