UNION,INTERSECT and EXCEPT

I will explain these by taking an example:

CREATE TABLE OrderDetail
(
ID INT Primary Key NOT NULL IDENTITY(1,1),
NAME NVARCHAR(100),
Price INT,
Quantity INT
)
Insert some records:
INSERT INTO OrderDetail VALUES('Biscuit','30',2)
INSERT INTO OrderDetail VALUES('Pen','10',1)
INSERT INTO OrderDetail VALUES('physics Book','100',1)
INSERT INTO OrderDetail VALUES('Chemistry Book','120',1)
INSERT INTO OrderDetail VALUES('Math Book','90',1)
INSERT INTO OrderDetail VALUES('Note Book','20',5)
INSERT INTO OrderDetail VALUES('Mechanics Book','20',5)
INSERT INTO OrderDetail VALUES('Mechanics Book','20',6)

UNION:
We can union two result set with same structure.
(SELECT ID,Name FROM OrderDetail where Quantity=1) UNION (SELECT ID,Name FROM OrderDetail where Quantity=5)
Result :

ID name
2 Pen
3 physics Book
4 Chemistry Book
5 Math Book
6 Note Book
7 Mechanics Book

INTERSECT:
We can union two result set with same structure.
(SELECT Name FROM OrderDetail where Quantity=6) INTERSECT (SELECT Name FROM OrderDetail where Quantity=5)
Result :

name
Mechanics Book