获取有奖金的员工相关信息

CREATE TABLE `employees` (
`emp_no` int(11) NOT NULL,
`birth_date` date NOT NULL,
`first_name` varchar(14) NOT NULL,
`last_name` varchar(16) NOT NULL,
`gender` char(1) NOT NULL,
`hire_date` date NOT NULL,
PRIMARY KEY (`emp_no`));
CREATE TABLE `dept_emp` (
`emp_no` int(11) NOT NULL,
`dept_no` char(4) NOT NULL,
`from_date` date NOT NULL,
`to_date` date NOT NULL,
PRIMARY KEY (`emp_no`,`dept_no`));
create table emp_bonus(
emp_no int not null,
recevied datetime not null,
btype smallint not null);
CREATE TABLE `salaries` (
`emp_no` int(11) NOT NULL,
`salary` int(11) NOT NULL,
`from_date` date NOT NULL,
`to_date` date NOT NULL, PRIMARY KEY (`emp_no`,`from_date`));

-- 一般答案
select eb.emp_no,e.first_name,e.last_name,eb.btype,s.salary,(s.salary*btype*0.1) bonus from emp_bonus eb,employees e,salaries s where eb.emp_no = e.emp_no and eb.emp_no = s.emp_no and s.to_date = '9999-01-01'

-- 利用条件判断解法
select eb.emp_no,
       e.first_name,
       e.last_name,
       eb.btype,
       s.salary,
       (case btype
           when 1 then s.salary*0.1
           when 2 then s.salary*0.2
           when 3 then s.salary*0.3
           end
           ) bonus
from emp_bonus eb,
     employees e,
     salaries s
where eb.emp_no = e.emp_no
  and eb.emp_no = s.emp_no
  and s.to_date = '9999-01-01'

case colume 
    when condition then result
    when condition then result
    when condition then result
    else result
end