sql的一个小问题

[guanzx]

TITLE(Name, ISBN, CallNumber, Year, AuthorFName, AuthorLName);
PK(CallNumber)


Add the constraint that ISBN and Name fields are alternate keys in the TITLE table and that they cannot take a NULL value

应该怎么写？

[csdyyr]

alter table TITLE
  alter column ISBN varchar(100) not null

alter table TITLE
  alter column Name varchar(100) not null

alter table TITLE 
  add constraint alt_key unique(ISBN,Name)