- Relational Algebra:
- Relational Algebra =
a mathematical language
for manipulating
relations
Recall that:
- Relation = a
subset of
a cartesian product
(So a relation is a set !!!!)
- Relation = a
subset of
a cartesian product
- Relational Algebra =
a mathematical language
for manipulating
relations
- Relational Algebra contains
the following
oeprators:
- Set operators
- Relational database specific operators
- set functions
Overview of the operators in Relational Algebra:
- Very important facts:
- The input(s) of
a Relational Algebra
operator is/are:
- one or more relations
(A relation = a set of tuples (table))
- The result (= output)
of a Relational Algebra
operation
is always:
- a relation
- Graphically:
- The input(s) of
a Relational Algebra
operator is/are:
- This property is
necessary so that
we can use
Relational Operators
in a cascaded (chained) manner:
- It is similar to
why we
can cascade the
add (arithmetic) operations:
The add operation works on 2 numbers and outputs a number: 3 + 5 = 8 (number + number = number)
We can cascade the addition because the result of an addition is always a number: 3 + 5 + 9 = 8 + 9 = 17
(If 3 + 5 did not result in a number, we could not continue
with the arithmetic operation !!!)