dbms

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Database System Concepts
Chapter 2:Introduction to the Relational
Model
 Structure of Relational Databases
 Database schema
 Keys
 SQL

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

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Database System Concepts

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Database System Concepts
 Relation
 Tuple
 Attribute
 Relation schema
 Relation instance
 Degree
 Cardinality
 Domain
 Atomic
 Null Values

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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

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Database System Concepts
 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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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts
Keep email as one of the superkey
above,,,,

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts
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.

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts

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Database System Concepts
Primary key

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

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Database System Concepts