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# Relational Algebra Overview

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@FinestPlutonium

### What is the PROJECT operation denoted by?

• π (pi) (correct)
• σ (sigma)
• ρ ( rho )
• λ (lambda)
• ### What does the PROJECT operation do to the columns of a relation?

• It renames certain columns
• It removes certain columns and keeps the others
• It keeps certain columns and discards the others (correct)
• It rearranges certain columns
• ### What is the main purpose of the PROJECT operation?

• To combine two relations
• To remove duplicate tuples from a relation
• To select specific columns from a relation (correct)
• To reorder the columns of a relation
• ### What is the result of applying the PROJECT operation to a relation?

<p>A relation with certain columns removed</p> Signup and view all the answers

### What is an alternative term for the PROJECT operation?

<p>SELECT</p> Signup and view all the answers

### What is a relation in a relational model based database?

<p>A table in the database</p> Signup and view all the answers

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

<p>How two tables are connected together</p> Signup and view all the answers

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

<p>Table and connection between tables</p> Signup and view all the answers

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

<p>To store and manage data</p> Signup and view all the answers

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

<p>To establish connections between tables</p> Signup and view all the answers

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

<p>It is always less than or equal to the number of tuples in R</p> 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?

<p>If the list of attributes includes a key of R</p> Signup and view all the answers

### Is the PROJECT operation commutative?

<p>No, the PROJECT operation is not commutative</p> Signup and view all the answers

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

<p>π contains the attributes in</p> Signup and view all the answers

### What is the purpose of the PROJECT operation?

<p>To select certain attributes from a relation</p> Signup and view all the answers

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

<p>The relations have the same number of attributes.</p> Signup and view all the answers

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

<p>They must have the same number of attributes.</p> Signup and view all the answers

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

<p>The relations have the same database.</p> Signup and view all the answers

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

<p>To ensure the relations have the same number of attributes.</p> 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?

<p>To ensure the union operation is valid.</p> Signup and view all the answers

### What does the INTERSECTION operation (∩) produce?

<p>A relation with tuples that are in both R and S</p> Signup and view all the answers

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

<p>They must be type compatible</p> Signup and view all the answers

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

<p>The same as the attribute names in R</p> Signup and view all the answers

### What is the symbol used to denote the INTERSECTION operation?

<p>∩</p> Signup and view all the answers

### What is the result of R ∩ S?

<p>A relation with tuples that are in both R and S</p> 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".

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## 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.

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