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-- 1.  查询员工表所有数据,并说明使用*的缺点 
 SELECT * from employees
 -- *号查询效率低
-- 2.  查询所员工的 email 全名,公司 email 统一以 "@qq.com " 结尾. 
 SELECT email from employees WHERE email like "%@qq.com"
-- 3.  打印公司里所有的 manager_id(去除重复数据) 
 select distinct manager_id from employees
-- 4.  查询职位(JOB_ID)为'ST_CLERK'的员工的工资 
 SELECT salary from employees WHERE JOB_ID="ST_CLERK"
-- 5.  查询 50 号部门的员工姓名. 
 SELECT last_name from employees WHERE department_id=50
-- 6.  查询 80 号部门工资大于 7000 的员工的全名. 
 SELECT first_name,last_name from employees WHERE department_id=50 and salary>7000
-- 7.  查询工资高于 7000 但是没有提成的所有员工. 
 SELECT * from employees WHERE commission_pct=null and salary>7000
 -- 8.  查询入职日期在 1997-5-1 到 1997-12-31 之间的所有员工信息 
 -- SELECT * from employees WHERE hiredate between '1997-5-1' and '1997-12-31'
 select *
 from employees
 where hiredate between str_to_date('1997-5-1','%Y-%m-%d') and str_to_date('1997-12-31','%Y-%m-%d')
-- 9.  显示姓名中没有'L'字的员工的详细信息 
 SELECT * from employees WHERE first_name not like "%L%"
-- 10.  查询电话号码以 8 开头的所有员工信息. 
 SELECT * from employees WHERE phone_number like "8%"
-- 11.  查询 80 号部门中 last_name 以 n 结尾的所有员工信息 
 SELECT * from employees WHERE department_id=80 and last_name like "%n"
-- 12.  查询所有 last_name 由四个以上字母组成的员工信息 
 SELECT * from employees WHERE  first_name like '____'
 select  * from employees where LENGTH(last_name)>4
-- 13.  查询 first_name 中包含"na"的员工信息. 
 SELECT * from employees WHERE  first_name like '%na%'
-- 14.  显示公司里所有员工的工资级别 case when 
 select employee_id, salary,
     CASE
         when salary>=15000 then'D'
         when salary>=8001 or salary>=15000 then'B'
         when salary>=5001 or salary>=8000 then'A'
         else 'A'
 END as '工资标准'
  from employees
  
  -- 15 根据入职时间打印出员工级别 
  select hiredate,
         case 
             when date_format(hiredate,'%Y')>1990  then '新员工' 
             when date_format(hiredate,'%Y')>=1986 then'普通员工' 
             when date_format(hiredate,'%Y')<=1985  then '资深员工'
 end as 员工级别
 from employees
  
 --  请打印出 1997 年入职的员工
 select first_name from employees where date_format(hiredate,'Y')=1978
  
 --  把 hiredate 列看做是员工的生日,求本月过生日的员工
 select * from employees where date_format(now(),'%m')=date_format(hiredate,'%m')
  
 --  查询入职时间超过25年的员工信息
 select * from employees where date_format(now(),'%Y')-date_format(hiredate,'%Y')>'25'
--  以  员工id-员工完整姓名-员工工资  的形式查询员工信息
 select employee_id,salary,concat(first_name,last_name) from employees
  
 --  查询工资高于10000并且岗位id长度小于5的员工信息
 select * from employees where salary>10000 and length(job_id)<=5
  
  
