ch2_jayarao.ppt

©Silberschatz, Korth and Sudarshan
1.1
Database System Concepts
Chapter 2:Introduction to the Relational
Model
 Structure of Relational Databases
 Database schema
 Keys
 SQL

1.2
 A relational database consists of a collection of tables, each of
which is assigned a unique name. For example, consider the
instructor table

1.3

1.4
 Relation
 Tuple
 Attribute
 Relation schema
 Relation instance
 Degree
 Cardinality
 Domain
 Atomic
 Null Values

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1.6

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1.13
 The null value is a special value that signifies that the value is
unknown or does not exist.

1.14

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1.19
Keys
 A superkey is a set of one or more attributes that, taken collectively,
allow us to identify uniquely a tuple in the relation.

1.20
 Candidate keys are super keys for which no proper subset is a
super key. Such minimal super keys are called candidate keys.

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1.24
Keep email as one of the superkey
above,,,,

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1.31
Foreign key
 It is an attribute in the table which refers the primary key
of the another table
 It is used to link the two tables together.
 Maintains referential integrity.

1.32

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1.39
Primary key

1.40
Alternate/secondary key
 All candidate key other than the primary key.
 Unique key :all candidate key which can support null values

1.41

ch2_jayarao.ppt

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