add constraint fk
ALTER TABLE Orders
ADD CONSTRAINT FK_PersonOrder
FOREIGN KEY (PersonID) REFERENCES Persons(PersonID);add constraint fk
ALTER TABLE Orders
ADD CONSTRAINT FK_PersonOrder
FOREIGN KEY (PersonID) REFERENCES Persons(PersonID);foreign key
Foreign Key:
It is a column that comes from a different table and
using Foreign key tables are related each other
It is the primary key of another table
It can be duplicate or null for another table
Primary Key :
It is unique column in every table in a database
It can ONLY accept;
- nonduplicate values
- cannot be NULL
Unique Key:
Only unique value and also can contain NULLwhat is foreign key
Foreign Key:
It is a column that comes from a different table and
using Foreign key tables are related each other
It is the primary key of another table
It can be duplicate or null for another tableWhat is foreign key?
Foreign Key is a non-key attribute which is derived from the primary key
of another table which links those tables together.Copyright © 2021 Codeinu
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