Keys in dbms
- 2. Indroduction What Is Keys? *keys are very important part of relational data base. *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. DBMS has five types of keys in it and they all has different functionality. The keys are all follows: *Super key *Candidate key *Primary key *Foreign key *Composite key
- 4. Super key: A super key is a set of ONE or MORE columns(Attributes) to uniquely identify rows in a table.
- 5. Examples: Super keys: Empssn Empnum Empssn,empna me Empssn,num,na me Empnum,name Empssn Empnum Empname 9876540098 Ca05 Shana 9876543210 Ca06 Shalini 1234567890 Ca07 Bhavani 2143658709 Ca08 Suvathi 6543210987 Ca09 Nithya
- 6. Candidate key: *A SUPER KEY with no redundant attribute is known as Candidate Key.
- 7. Candidate keys : *Empssn *Empnum Empssn Empnum Empnam e 98765400 98 Ca05 Shana 987654321 0 Ca06 Shalini 123456789 0 Ca07 Bhavani 214365870 9 Ca08 Suvathi 654321098 7 Ca09 Nithya
- 8. Primary key: *A Primary key is a column or set of columns in a table that uniquely identifies tubels(rows) in that table.
- 9. Example: Empssn Empid Empnam e 98765400 98 Ca05 Shana 98765432 10 Ca06 Shalini 12345678 90 Ca07 Bhavani 21436587 09 Ca08 Suvathi 65432109 87 Ca09 Nithya Empssn Empnum Empnam 987654009 8 Ca01 Oviya 907856341 2 Ca02 Raiza 123456789 0 Ca03 Bindhu 543210987 6 Ca04 Kajal 654321098 7 Ca10 Pragya
- 10. Foreign key: *Foreign key are column of a table that points to the primary key of another table. *They act as a cross reference between tables.
- 11. Example: emp 1 emp 2 Empssn Empid Empnam e 98765400 98 Ca05 Shana 98765432 10 Ca06 Shalini 12345678 90 Ca07 Bhavani 21436587 09 Ca08 Suvathi 65432109 87 Ca09 Nithya Empssn Empnum Empnam 987654009 8 Ca01 Oviya 907856341 2 Ca02 Raiza 123456789 0 Ca03 Bindhu 543210987 6 Ca04 Kajal 654321098 7 Ca10 Pragya
- 12. Composite key: *A key that consists of more than one atributes to uniquely identify rows(also known as records or tubels)in a table is called COMPOSITE KEY.
- 13. Example : Empssn Empnum Empname 9876543210 Ca05 Shana 1234567890 Ca06 Shalini 9078534127 Ca07 Bhavani 2143658709 Ca08 Suvathi 5432109876 Ca09 Nithya