Database keys
- 1. Database Keys Presented by Rahul Mishra
- 2. Database keys Keys are very important part of Relational database. They are used to establish and identify relation between tables. They also ensure that each record within a table can be uniquely identified by combination of one or more fields within a table.
- 3. Types:- 1. Primary Key 2. Candidate Key 3. Alternate Key 4. Composite 5. Super Key 6. Foeign Key
- 4. 1. Super Key Emp_code Name Address Dept_ID It is an attribute or an set of attribute whose combined value uniquely identifies a tuple within a relation. {Emp_code, Name, Address, Dept_ID}, {Emp_code, Name, Address}, {Name, Address}, {Emp_code}, etc.
- 5. 2. Candidate Key Emp_code Name Address Dept_ID It is a minimal super key i.e., a super key which does not have any proper subset which is also a super key. {Emp_code} and {Name, Address}
- 6. 3. Primary Key Emp_code Name Address Dept_ID A candidate key which is actually chosen by database designer as the means of uniquely identifying the tuple within a relation. {Emp_code}
- 7. 4. Alternate Key Emp_code Name Address Dept_ID All candidate keys which are not chosen as a primary key is called an alternate key. {Name, Address}
- 8. 5. Composite Key Emp_code Name Address Dept_ID A primary key formed by combination of one or more attributes. {Name, Address}
- 9. 6. Foreign Key Emp_code Name Address Dept_ID A foreign key is a field (or collection of fields) in one table that uniquely identifies a row of another table or the same table. Department Dept_ID Dept_Name Employee Dept_ID – Primary Key in Department Table Foreign Key in Employee Table
- 10. Thank You! Here is a potato for you!!!