Keys are important parts of relational databases that establish relationships between tables and uniquely identify records. There are five types of keys: super keys use one or more fields to identify rows, candidate keys are super keys without redundant attributes, primary keys uniquely identify rows in a table, foreign keys link tables by pointing to a primary key, and composite keys use more than one attribute to uniquely identify rows.

1. 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,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