PDF Notes: Database Lec 6 Slides

What are unary operations in relational algebra?

They operate on one relation, such as select, project, and rename.

What are binary operations in relational algebra?

They operate on pairs of relations, like union, set difference, and Cartesian product.

What does the union operation do?

It combines rows from two relations into one, removing duplicates.

What conditions must be met for a union operation to be valid?

Relations must have the same arity and compatible domains.

How does the set-difference operation work?

It finds tuples in one relation that are not in another.

What are the requirements for a set-difference operation to be valid?

Both relations must have the same arity and compatible domains.

What does the Cartesian product operation do?

It pairs every tuple from one relation with every tuple from another.

What problem arises with the Cartesian product operation?

Ambiguity occurs if both relations have attributes with the same name.

What is the purpose of the natural-join operation?

It combines two relations based on common attributes, simplifying queries.

What does the set-intersection operation find?

It identifies tuples that exist in both relations.

What is the assignment operation in relational algebra?

It assigns parts of a relational-algebra expression to temporary relation variables.