![]() People pursuing Database studies should be aware of the Keys in DBMS. It also helps in avoiding redundancy and is managed by the DBA. Keys in DBMS are essential and play a vital role in managing the database and accessing the data in a well-mannered form. In simple terms, Referential Integrity is achieved by Foreign Keys in DBMS. This type of inheritance is known as Referential Integrity and is known as Foreign Keys in DBMS relations. The dept_code attribute of the student table is inherited from the Dept_code of the Department Table. S_IDįrom these two tables, the Student Table is dependent on the Department Table as Student Table can only have those records from which the department exists in the Department Table. Let us understand this by example by taking 2 tables Student and Department. This is the last key in the article on Keys in DBMS. Foreign Key in DBMSįoreign Key in DBMS is different from all the Key in DBMS which is being discussed till now, as Foreign key is applicable on 2 tables. Salary cannot be a super key as the same salary for more than 1 employee is possible, and Phone can also not be a super key as the employee may have a phone number or not, possible to have null values.Īlso, the combination of the super keys is possible in this table the possible super key is: In the above table, ID is a super key as it will be always unique because the employee ID for every employee is different and unique, Name cannot be a super key as the same name is possible for 2 different people. Super Key may contain extraneous attributes. The super key attribute can be NULL, which means its values can be null. On the other hand, all candidate keys are super keys. It is not at all compulsory that all super keys are candidate keys. It is the subset or the part of the Super key. This is the first key in the article Keys in DBMS. It is the superset of all such attributes that can uniquely identify the table. Super Key will not be NULL and will always be unique. It is used to uniquely identify the tuple. Super Key is like a superset, from which another key can be derived. Let’s understand each of the Keys in DBMS one by one, Super Key in DBMS There are different types of Keys in DBMS available and they are: ![]() In short, Keys in DBMS are required to identify the tuples uniquely. You can query like increment the salary of a person by 10% whose ID is 1004. The query can be written easily with the help of Keys in DBMS. the ID column in the Employee table is the key which will be unique for every single entry getting created in the database. So, as per the given query, this will increment the salary of both John, which is wrong. But still there can be a narrow chance of duplicate row.As you can see, the Employee table has 2 entries by the name John and they are referring to two different people. ![]() Like if there is no EmployeeID or SSN columns, then you can make FullName + DateOfBirth as Composite primary Key. Composite Key: If a table do have a single columns that qualifies for a Candidate key, then you have to select 2 or more columns to make a row unique. Super Key: If you add any other column/attribute to a Primary Key then it become a super key, like EmployeeID + FullName is a Super Key.ĥ. Alternate Key: Candidate column other the Primary column, like if EmployeeID is PK then SSN would be the Alternate key.Ĥ. ![]() Here in Employee table you can choose either EmployeeID or SSN columns, EmployeeID is preferable choice, as SSN is a secure value.ģ. Primary Key: is the columns you choose to maintain uniqueness in a table. Here in Employee table EmployeeID & SSN are Candidate keys.Ģ. Candidate Key: are individual columns in a table that qualifies for uniqueness of all the rows. ![]()
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