36 - 按分类统计薪水

-- 方法一
select
    'Low Salary' category,sum(income <20000) accounts_count 
from
    Accounts     
union
select
    'Average Salary' category,sum(income between 20000 and 50000) accounts_count 
from
    Accounts    
union
select
    'High Salary' category,sum(income>50000) accounts_count 
from
    Accounts ;

-- 方法二

select
    'Low Salary' category,count(*) accounts_count 
from
    Accounts 
where
    income <20000
union
select
    'Average Salary' category,count(*) accounts_count 
from
    Accounts 
where
    income between 20000 and 50000
union
select
    'High Salary' category,count(*) accounts_count 
from
    Accounts 
where
    income>50000;