Question

From here

ALTER TABLE ORDERS
ADD FOREIGN KEY (customer_sid) REFERENCES CUSTOMER(SID); 

How do I add several keys with SQL Server? Is it something like the below? (I cant test ATM and unfortunately I have no way to test queries unless I run it through code)

ALTER TABLE ORDERS
ADD FOREIGN KEY (customer_sid) REFERENCES CUSTOMER(SID), 
ADD FOREIGN KEY (customer_sid2) REFERENCES CUSTOMER(SID2);

or is it like

ALTER TABLE ORDERS
ADD FOREIGN KEY (customer_sid, customer_sid2) REFERENCES CUSTOMER(SID, SID2)

Answer 1

The second code block from your question:

ALTER TABLE ORDERS 
ADD FOREIGN KEY (customer_sid) REFERENCES CUSTOMER(SID),  
ADD FOREIGN KEY (customer_sid2) REFERENCES CUSTOMER(SID2); 

will take care of what you are trying to do.