摘要： select * ,sum(salary) over(partition by dname order by hiredate) from employee;可以用于求公司的开支 select * ,sum(salary) over(partition by dname order by hired 阅读全文

摘要： 格式： row_number() | rank() | dense_rank() over { partition by ... order by ... } //itheima数据库的employee表 select dname , ename, salary, row_rank() over ( 阅读全文

摘要： select *,if(socre >=85,'优秀','及格') flag from score; select ifnull(5,0); //如果是5则返回5 是NULL则返回0 1.select case 5 when 1 then '你好' when 2 then 'hello' when 阅读全文