http://www.w3schools.com/sql/sql_foreignkey.asp
To create a FOREIGN KEY constraint on the "P_Id" column when the "Orders" table is already created, use the following SQL:
ALTER TABLE Orders
ADD FOREIGN KEY (P_Id)
REFERENCES Persons(P_Id)
To allow naming of a FOREIGN KEY constraint, and for defining a FOREIGN KEY constraint on multiple columns, use the following SQL syntax:
ALTER TABLE Orders
ADD CONSTRAINT fk_PerOrders
FOREIGN KEY (P_Id)
REFERENCES Persons(P_Id)
One has the keyword "constraint", the other no.
I can't figure it out the difference.
I think that the first one is enough for the normal query.
About Foreign Key Constraint
Posted - 03/08/2013 : 13:46:37
