Relational Calculus
Tuple Relational Calculus
It is a non-procedural query language
This means that it will mention the required information without specifying the procedure to obtain it
An expression in tuple relational calculus is denoted as follows: {t | P(t)}
In other words, it is the set of all tuples t such that predicate P is true for t
t is a tuple variable and t[A] denotes the value of tuple t for attribute A
The predicate can contain:
A set of attributes and constants
A set of comparison operators: (<, ≤, =, ≠, >, ≥)
A set of connectives: and (∧), or (v)‚ not (¬)
An implication (⇒): x ⇒ y, i.e. if x if true, then y is true
x ⇒ y ≡ ¬x v y
A set of quantifiers:
Ex. Finding ID, name, dept_name and salary of all instructors who have salary greater than 80000: {t | t ∈ instructor ∧ t [salary] > 80000}
Domain Relational Calculus
It is a non-procedural language as well
It is as powerful as tuple relational calculus
Ex. Finding ID, name, dept_name and salary of all instructors who have salary greater than 80000:
{<i, n, d, s> | <i, n, d, s> ∈ instructor ∧ s > 80000}
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