Calculus vs. Algebra

Relational Algebra

Relational Algebra is a procedural query language Based on algebraic concepts.
It defines Operations on relations that produce a new relation as a result

Tuple Relational Calculus (used by SQL)

The tuple relational calculus is a nonprocedural language,
relational algebra is procedural.

We must provide a formal description of the information desired.
A query in the tuple relational calculus is expressed as:

{t| P(t)} i.e. the set of tuples t for which predicate P is true.

The tuple relational calculus (restricted to safe expressions)
is equivalent in expressive power to the relational algebra.