sql union 语句

1：Union语句: 把两个结果合为一体(但是完全重复的数据会去掉)

Eg1: select name, age, ‘学生无工资’ from student

       union  

       select name, age, sal from teacher

Eg2: select top 2  CONVERT(varchar(20),itemId) itemid, fee, addDate  from Orders

union

select ‘合计‘,SUM(fee),GETDATE() from (select top 2 fee  from Orders) a

2：Union All (重复的数据不会去掉)

工资合计效果：Select  name, sal  from  teacher

                          union all

select  ‘工资合计’,  sum(sal)  from  teacher