SQL3 questions.pdf - Databases - Relational Algebra and SQL...

Databases - Relational Algebra and SQL 3
Jianxin Li
School of Computer Science & Software Engineering
University of Western Australia
Jianxin Li (UWA) Lab 4 1 / 6

Relational Algebra
Some of the answers will require you to type relational algebra expressions
such as
π
id
( σ
( a > 10 )
(( R ./ S ) × T )) (1)
To write these in text, do the following
Use the words rho, pi and sigma for ρ , π and σ
Use an underscore for subscripts
Use the word bowtie for ./ and the letter x for ×
So you will type: pi_id(sigma_(a > 10) ((R bowtie S) x T))
Jianxin Li (UWA) Lab 4 2 / 6

Relational Algebra
The first few questions will use a student, unit, grade database similar to the
one from lectures, but where the tables are called S (for student), U (for unit)
and G (for grade) and have the following schema:
S(sid, name, gender)
U(uid, name)
G(sid, uid, grade)
Students have a unique id, a name and a gender (either M or F) , Units have an
unique id (like CITS1402) and a name (like Databases), while Grades indicate
what grade the student with id sid achieved when they took the unit with id
uid.