What is functional dependency in SQL?

What is functional dependency explain?

A functional dependency (FD) is a relationship between two attributes, typically between the PK and other non-key attributes within a table. For any relation R, attribute Y is functionally dependent on attribute X (usually the PK), if for every valid instance of X, that value of X uniquely determines the value of Y.

What do you mean by functional dependency in a database?

Functional Dependency (FD) is a constraint that determines the relation of one attribute to another attribute in a Database Management System (DBMS). Functional Dependency helps to maintain the quality of data in the database. … A functional dependency is denoted by an arrow “→”.

What is functional dependency explain how do you use it?

Functional Dependency (FD) determines the relation of one attribute to another attribute in a database management system (DBMS) system. Functional dependency helps you to maintain the quality of data in the database. … The functional dependency of X on Y is represented by X → Y.

What are the main characteristics of functional dependency?

Main characteristics of functional dependencies used in normalization:

  • have a 1:1 relationship between attribute(s) on left and right-hand side of a dependency;
  • hold for all time;
  • are nontrivial.
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Which is the correct form of functional dependency?

A key dependency is a functional dependency of the form X → U. Then X is called a superkey for relation R. If there is no proper subset Y of X such that Y is a superkey, then X is called a key.

How do you write a functional dependency in DBMS?

A functional dependency is a constraint that specifies the relationship between two sets of attributes where one set can accurately determine the value of other sets. It is denoted as X → Y, where X is a set of attributes that is capable of determining the value of Y.

For example,

roll_no name age
45 abc 19

What does the functional dependency XY mean?

In other words, a dependency FD: X → Y means that the values of Y are determined by the values of X. Two tuples sharing the same values of X will necessarily have the same values of Y.

What is multivalued dependency with example?

Multivalued dependency occurs when there are more than one independent multivalued attributes in a table. For example: Consider a bike manufacture company, which produces two colors (Black and white) in each model every year.

What is unique role assumption?

Explanation: Unique role assumption means that the attribute names must have unique meaning in the database. This prevents us from using the same attribute to mean different things in different schemas. … Explanation: The value of the data at a particular time is called as a snapshot.

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