常用查询2

------新列(总收入)
select u_Name "姓名",(u_Phone+u_XinZi) "总收入" from User_Info;
------排序
select * from User_Info order by u_Name asc; --升序
select * from User_Info order by u_XinZi desc; --降序
select * from User_Info order by u_Id asc,u_XinZi desc;--一升一降
------空判断 is null
select * from User_Info where u_XinZi is null or u_XinZi < 1000;
------截取字符串
select subStr(u_Name,0,3) from User_Info;
------子查询
select * from User_Info where u_Dept = (select d_Id from User_Dept where d_Name = '开发');
------内连接查询联查
select * from User_Info,User_Dept where u_Dept = d_Id;--普通链接
select * from User_Info inner join User_Dept on(i_Dept = d_Id);--内连接
select * from User_Info left join User_Dept on(i_Dept = d_Id);--左外连接
select * from User_Info right join User_Dept on(i_Dept = d_Id);--右外连接
select * from User_Info full join User_Dept on(u_Dept = d_Id);--完全外连接
select * from User_Info cross join User_Dept;--交叉连接
------添加外键关系
alter table User_Info add constraint FK_User_Dept_User_Info foreign key(u_Dept) references
User_Dept(d_Id);
------交集运算
intersect运算:查询两张表中相同数据的记录 
select job from 部门1
intersect
select job from 部门2
------差集运算
minus运算： 返回第一张表减去两张表的交集的剩下部分
在部门1中有，而在部门2中没有的工种
select job from 部门1
minus 
select job from 部门2;