1 select *from 
 2 (select count(sal) as "工资1000-" from emp where sal < 1000) ,
 3 (select count(sal) as "工资1000-3000" from emp where sal > 1000 and sal <= 3000) ,
 4 (select count(sal) as "工资3000-4000" from emp where sal > 3000 and sal <= 4000) ,
 5 (select count(sal) as "工资4000+" from emp where sal > 4000) ;
 6 
 7  
 8 select  '1000-' as 工资区间,count(sal) as 人数 from emp where sal < 1000
 9 union
10 select  '1000-3000' as 工资区间, count(sal) as 人数 from emp where sal > 1000 and sal <= 3000
11 union
12 select  '3000-4000' as 工资区间, count(sal) as 人数 from emp where sal > 3000 and sal <= 4000
13 union
14 select  '4000+' as 工资区间,count(sal) as 人数 from emp where sal > 4000
15 
16 
17 select e.工资区间,count(工资区间) as 人数 from
18 (select case
19 when sal < 1000 then '1000-'
20 when sal > 1000 and sal <= 3000 then '1000-3000'
21 when sal > 3000 and sal <= 4000 then '3000-4000'
22 when sal > 4000 then  '4000+'
23 end as "工资区间"
24 from emp)e
25 group by e.工资区间