多表查询

1、财务部门的收入总和；select sum(incoming) from (select *from dept inner join emp ondept.dept1=emp.dept2)t where dept1=101;

2、It技术部入职员工的员工号 select sid from  (select *from dept inner join emp ondept.dept1=emp.dept2)t where dept1=103;
3、列出每一个部门中年纪最大的员工姓名，部门名称； selectname,dept_name from (select *from dept inner join emp on dept.dept1=emp.dept2)tgroup by dept1 order by age desc limit 1 ;/列出每个部门最大年纪;

4、列出每一个部门的员工总收入及部门名称；select dept_name ,sum(incoming) from (select *from dept inner joinemp on dept.dept1=emp.dept2)t group by dept1;

5、列出部门员工收入大于7000的部门编号，部门名称；select dept1 ,dept_name from (select*from dept inner join emp on dept.dept1=emp.dept2)t where incoming >7000 groupby dept1;
6、找出哪个部门还没有员工入职；select dept_name from (select*from dept left join emp on dept.dept1=emp.dept2)t where name is null;