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);alter table add column and foreign key mysql
ALTER TABLE database.table
ADD COLUMN columnname INT DEFAULT(1),
ADD FOREIGN KEY fk_name(fk_column) REFERENCES reftable(refcolumn) ON DELETE CASCADE;sql foreign key
CREATE TABLE orders (
id int NOT NULL,
user_id int,
product_id int,
PRIMARY KEY (id),
FOREIGN KEY (user_id) REFERENCES users(id),
FOREIGN KEY (product_id) REFERENCES products(id)
);foreign key
CREATE TABLE Employee(
EmployeeID int NOT NULL,
LastName varchar(50) NOT NULL,
FirstName varchar(20) NOT NULL,
Age int,
DeptNo int,
PRIMARY KEY (EmployeeID),
FOREIGN KEY (DeptNo) REFERENCES Department(DeptNo)
);what 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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