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) );
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) );
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 NULL
foreign key constraint
CREATE TABLE Students ( /* Create table with foreign key - Way 1 */ ID INT NOT NULL Name VARCHAR(255) LibraryID INT PRIMARY KEY (ID) FOREIGN KEY (Library_ID) REFERENCES Library(LibraryID) ); CREATE TABLE Students ( /* Create table with foreign key - Way 2 */ ID INT NOT NULL PRIMARY KEY Name VARCHAR(255) LibraryID INT FOREIGN KEY (Library_ID) REFERENCES Library(LibraryID) ); ALTER TABLE Students /* Add a new foreign key */ ADD FOREIGN KEY (LibraryID) REFERENCES Library (LibraryID);
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 table
What 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
Forgot your account's password or having trouble logging into your Account? Don't worry, we'll help you to get back your account. Enter your email address and we'll send you a recovery link to reset your password. If you are experiencing problems resetting your password contact us
