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
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