Keys in dbms

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1. Keys In DBMS Presented by Shalini

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,empname Empssn,num,name 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 Empname 9876540098 Ca05 Shana 9876543210 Ca06 Shalini 1234567890 Ca07 Bhavani 2143658709 Ca08 Suvathi 6543210987 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 Empname 9876540098 Ca05 Shana 9876543210 Ca06 Shalini 1234567890 Ca07 Bhavani 2143658709 Ca08 Suvathi 6543210987 Ca09 Nithya Empssn Empnum Empnam 9876540098 Ca01 Oviya 9078563412 Ca02 Raiza 1234567890 Ca03 Bindhu 5432109876 Ca04 Kajal 6543210987 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 Empname 9876540098 Ca05 Shana 9876543210 Ca06 Shalini 1234567890 Ca07 Bhavani 2143658709 Ca08 Suvathi 6543210987 Ca09 Nithya Empssn Empnum Empnam 9876540098 Ca01 Oviya 9078563412 Ca02 Raiza 1234567890 Ca03 Bindhu 5432109876 Ca04 Kajal 6543210987 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