Uniqueness Of Names

hi

am new to sql...i need to write a query ..it is like two teams can play more than 1 game but on different dates..


so if i create the table like this

Create Table Games( TeamName1 char(30),
2 numGoals1 int,
3 TeamName2 char(30),
4 numGoals2 int,
5 play_date char(10),
6 primary key(TeamName1,TeamName2,play_date),
7 Check(TeamName1!=TeamName2)
8 );

this violates the constraint if i give the two teams on the same date..how to give the condition such that it checks for the violation of condition if the team names are interchanged.. for eg

if i give the values as
Insert Into Games values('chelsea',1,'arsenal',2,'17-1-2000');
and
Insert Into Games values('arsenal',1,'chelsea',2,'17-1-2000');


the above should violate the constraint ..how to do it