The document defines and provides examples of different types of keys used in database systems, including super keys, candidate keys, primary keys, alternate keys, composite keys, foreign keys, and unique keys. A super key can identify a tuple but contains extra attributes, while a candidate key is a minimal super key. The primary key is chosen by the administrator and must be unique. Alternate keys are other candidate keys, and composite keys comprise multiple attributes. Foreign keys link tables using primary keys, and unique keys are like primary keys but allow null values.

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Types of Keys in Database System

2. Types of Keys
 Super Key
 Candidate Key
 Primary Key
 Alternate Key
 Composite Key
 Foreign Key
 Unique Key
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3. Super Key
 An attribute or set of attributes that are required to identifies a
tuple in a relation.
 A Super Key may contain additional attributes that are not
require for unique identification.
 Unique Key-Student_ID
 Super Key:
 {Student_ ID, Student_Name}
 {Studenr_ID, Student_Address}
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4. Candidate Key
 Candidate Keys are minimal set of Super Key
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5. Primary Key
 Primary Key is a candidate key chosen by database administrator for
unique identification.
 No Two rows can have the primary key same values.
 Every row must have primary key value
 The primary key value can not be null
 Value in primary key can not be modified.
 Primary Key: PAN No.
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6. Alternate Key
• Candidate keys other than primary key are called as a alternate
key.
• PK: PAN No.
• Alternate Key: Voter Id No, Passport No
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7. Composite Key
• Composite key is the one having combination of more than one attribute
to uniquely determine the records/tuples in a table.
• The only condition that is necessary before choosing composite key is,
the attributes which are responsible for forming the composite key must
not be a key individually.
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8. Foreign Key
• A foreign key is nothing but an attribute that is commonly linked between two
relation using that same attribute and that attribute must be primary key from one
relation.
• Both the relations/tables must contain the same attribute.
• It can be referred as referential integrity
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9. Unique Key
 Unique key is same as primary key with the difference being
the existence of Null value.
 Unique Key: MemberID
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All Keys

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