25 Questions
What is the PROJECT operation denoted by?
π (pi)
What does the PROJECT operation do to the columns of a relation?
It keeps certain columns and discards the others
What is the main purpose of the PROJECT operation?
To select specific columns from a relation
What is the result of applying the PROJECT operation to a relation?
A relation with certain columns removed
What is an alternative term for the PROJECT operation?
SELECT
What is a relation in a relational model based database?
A table in the database
What does the term 'relationship' refer to in a relational model based database?
How two tables are connected together
What is the main difference between relation and relationship in DBMS?
Table and connection between tables
What is the role of a relation in a relational model based database?
To store and manage data
What is the primary function of a relationship in a relational model based database?
To establish connections between tables
What can be said about the number of tuples in the result of projection π(R)?
It is always less than or equal to the number of tuples in R
What is a condition under which the number of tuples in the result of PROJECT is equal to the number of tuples in R?
If the list of attributes includes a key of R
Is the PROJECT operation commutative?
No, the PROJECT operation is not commutative
What is the condition under which π(π(R)) = π(R)?
π contains the attributes in
What is the purpose of the PROJECT operation?
To select certain attributes from a relation
What is a necessary condition for a union operation to be valid?
The relations have the same number of attributes.
What is a requirement for relations r and s to be union-compatible?
They must have the same number of attributes.
Which of the following is NOT a condition for a valid union operation?
The relations have the same database.
What is the primary purpose of checking the number of attributes in a union operation?
To ensure the relations have the same number of attributes.
Why do relations r and s need to have the same number of attributes for a valid union operation?
To ensure the union operation is valid.
What does the INTERSECTION operation (∩) produce?
A relation with tuples that are in both R and S
What is a requirement for the two operand relations R and S?
They must be type compatible
What are the attribute names in the result of the INTERSECTION operation?
The same as the attribute names in R
What is the symbol used to denote the INTERSECTION operation?
∩
What is the result of R ∩ S?
A relation with tuples that are in both R and S
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".
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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