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;