高级函数-case

case函数 (适合区间,>,<判断)

   case when 判断表达式 then

        when 判断表达式 then

        .....

   end

 

  select deptno,count(*) total,

   sum(case when sal>=2000 then 1

       end) great,

   sum(case when sal<2000 then 1

       end) least

  from emp

  where deptno is not null

  group by deptno;

 

//统计部门中男人数和女人数

 create table j20(

  id number(7),

  name varchar(20),

  sex char(1), --'M'或'F'

  deptno number(7));

 

 select deptno,

        sum(decode(sex,'M',1,0)) as male,

        sum(decode(sex,'F',1,0)) as female

 from j20

 group by deptno;

 

 select deptno,

        sum(case when sex='M' then 1

            else 0 end) as male,

        sum(case when sex='F' then 1

            else 0 end) as female

 from j20

 group by deptno;

 //基于EMP表查询部门编号,工资1000以内人数,

 1000-2000人数,2000以上人数

 select deptno,

    sum(case when sal<1000 then 1

             else 0

        end) "1000以内",

    sum(case when sal>=1000 and sal<2000 then 1

             else 0

        end) "1000-2000",

    sum(case when sal>=2000 then 1

             else 0

        end) "2000以上"

 from emp

 group by deptno;

 

 //查询调薪结果，规则：MANAGER涨10%,CLERK涨20%,

  其他人涨5%

 select empno,ename,job,sal,

        decode(job,'MANAGER',sal*1.1,

                   'CLERK',sal*1.2,

                   sal*1.05) "加薪之后"

 from emp;