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What is SQL ?

Structured Query Language(SQL) is a special-purpose programming language designed for managing data in relational database management systems (RDBMS).


What is partial dependency ?

A Partial dependency is a dependency where A is functionally dependent on B( A -> B), but there is some attribute on A that can be removed from A and yet the dependency stills holds. For instance if the relation existed.

What is transitive dependency ?

Transitive dependency is a functional dependency which holds by virtue of transitivity. A transitive dependency can occur only in a relation that has three or more attributes. Let A, B, and C designate three distinct attributes (or distinct collections of attributes) in the relation.

Suppose all three of the following conditions hold:

 A -> B

 It is not the case that B ? A

 B ->C

Then the functional dependency A -> C (which follows from 1 and 3 by the  axiom of transitivity) is a transitive dependency.

What is candidate key, alternate key and composite key ?

A candidate key is one that can identify each row of a table uniquely. Generally a candidate key becomes the primary key of the table. If the table has more than one candidate key, one of them will become the primary key, and the rest are called alternate keys. A key formed by combining at least two or more columns is called composite key.

What is Normalization ?

Normalization is a process for assigning attributes to entities. It reduces data redundancies and helps eliminate the data anomalies.

Normalization works through a series of stages called normal forms:

First normal form (1NF)

Second normal form (2NF)

Third normal form (3NF)

Boyce-Codd Normal Form (BCNF)

The highest level of normalization is not always desirable.

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