自我总结的一引起SQL语句

--修改外键
ALTER TABLE dbo.titleauthor WITH NOCHECK ADD CONSTRAINT
 FK__titleauth__au_id__0519C6AF FOREIGN KEY
 (
 au_id
 ) REFERENCES dbo.authors
 (
 au_id
 ) ON UPDATE CASCADE
  ON DELETE CASCADE

--删除外键
ALTER TABLE dbo.titleauthor
 DROP CONSTRAINT FK__titleauth__au_id__0519C6AF

--创建联合键
create table t(  
  custid int,  
  custphone varchar(20),  
  orderquantity int,  
  custaddress varchar(20)  
  constraint Pk_t Primary Key(custid desc,custphone)
)