sqlserver三种数据集合运算

2.1   并集运算（UNION）

 (1)UNION ALL(不删除重复行) 

 Code:

1 SELECT empID,empName,position,degree
2 FROM Employees
3 UNION ALL
4 SELECT empID,empName,position,degree
5 FROM Sales

 (2)UNION(隐式DINSTINCT，删除重复行)

 Code:

1 SELECT empID,empName,position,degree
2 FROM Employees
3 UNION  
4 SELECT empID,empName,position,degree
5 FROM Sales

2.2 交集(INTERSECT)

 Code:

1 SELECT empID,empName,position,degree
2 FROM Employees
3 INTERSECT  
4 SELECT empID,empName,position,degree
5 FROM Sales

2.3  差集

Code:

1 SELECT empID,empName,position,degree
2 FROM Employees
3 EXCEPT  
4 SELECT empID,empName,position,degree
5 FROM Sales