## Questions and Answers

What is the PROJECT operation denoted by?

What does the PROJECT operation do to the columns of a relation?

What is the main purpose of the PROJECT operation?

What is the result of applying the PROJECT operation to a relation?

Signup and view all the answers

What is an alternative term for the PROJECT operation?

Signup and view all the answers

What is a relation in a relational model based database?

Signup and view all the answers

What does the term 'relationship' refer to in a relational model based database?

Signup and view all the answers

What is the main difference between relation and relationship in DBMS?

Signup and view all the answers

What is the role of a relation in a relational model based database?

Signup and view all the answers

What is the primary function of a relationship in a relational model based database?

Signup and view all the answers

What can be said about the number of tuples in the result of projection π(R)?

Signup and view all the answers

What is a condition under which the number of tuples in the result of PROJECT is equal to the number of tuples in R?

Signup and view all the answers

Is the PROJECT operation commutative?

Signup and view all the answers

What is the condition under which π(π(R)) = π(R)?

Signup and view all the answers

What is the purpose of the PROJECT operation?

Signup and view all the answers

What is a necessary condition for a union operation to be valid?

Signup and view all the answers

What is a requirement for relations r and s to be union-compatible?

Signup and view all the answers

Which of the following is NOT a condition for a valid union operation?

Signup and view all the answers

What is the primary purpose of checking the number of attributes in a union operation?

Signup and view all the answers

Why do relations r and s need to have the same number of attributes for a valid union operation?

Signup and view all the answers

What does the INTERSECTION operation (∩) produce?

Signup and view all the answers

What is a requirement for the two operand relations R and S?

Signup and view all the answers

What are the attribute names in the result of the INTERSECTION operation?

Signup and view all the answers

What is the symbol used to denote the INTERSECTION operation?

Signup and view all the answers

What is the result of R ∩ S?

Signup and view all the answers

## Study Notes

### Relational Algebra Overview

- In a relational model-based database, a "relation" refers to a table, while a "relationship" refers to the connection between two tables.

### Unary Relational Operations: PROJECT

- The PROJECT operation is denoted by π (pi) and keeps certain columns (attributes) from a relation, discarding the others.
- Properties of PROJECT operation:
- The number of tuples in the result of projection π(R) is always less than or equal to the number of tuples in R.
- If the list of attributes includes a key of R, then the number of tuples in the result of PROJECT is equal to the number of tuples in R.
- PROJECT is not commutative: π (π (R) ) = π (R) as long as contains the attributes in .

### Relational Algebra Operations from Set Theory: UNION

- For a union operation to be valid, the following conditions must hold:
- R and S must have the same number of attributes.

### Relational Algebra Operations from Set Theory: INTERSECTION

- INTERSECTION is denoted by ∩.
- The result of the operation R ∩ S is a relation that includes all tuples that are in both R and S.
- The attribute names in the result will be the same as the attribute names in R.
- The two operand relations R and S must be "type compatible".

## Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

## Description

Learn about the difference between relation and relationship in DBMS, including how they relate to tables and connections in a relational model based database.