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CS 111 – Nov. 10
• Structured Query Language (SQL)
– We’ve already seen simple select statements, with optional
“where” clause and aggregate functions.
– More example commands today
• Relational database
• Commitment
– Review for test after lab
Log in
• As you will see in lab, you first need to “log in” to the
database management system in order to see your
database.
• From a Web browser, go to cs.furman.edu/phpMyAdmin/
• Enter your database username & password
• (Demo)
• If your SQL commands are incorrect, you’ll get error
message.
Example
An abridged Employee table:
First
Last
Location
Title
Salary
Peter
Jacobs
Brussels
Broker
55000
Denise
Lambert
Brussels
Accountant
42500
Robert
Nijs
Brussels
Broker
66700
Ruth
Molloy
Chicago
Manager
68650
Declan
Murphy
Chicago
Accountant
84125
Susan
Patterson
Chicago
Economist
51000
Rachel
Brady
Cincinnati
Broker
43300
David
Cunningham
Cincinnati
Accountant
48000
John
Whelan
Cincinnati
Broker
60500
Yvonne
Butler
San Diego
Broker
48500
Veronica
Keating
San Diego
Broker
72000
Mary
Walsh
Dublin
Accountant
46850
Distinct
• Sometimes in SQL you have a lot of repeated data. And
you only want the values themselves, not the repetitions.
– Ex. 70, 70, 70, 80, 80, 80, 80, 80, 100  70, 80, 100
• Examples
select Test2 from Student;
gives all test grades
select distinct Test2 from Student;
only shows each value once
select distinct Test1, Test2 from Student;
finds distinct pairs. 70/60, 70/80, and 90/80 are
considered distinct.
Group by
• The “group by” clause is good at finding subtotals.
• Example: how many employees by job title:
– Select count(first) from Employee group by Title;
– Actually, doesn’t matter which field we count.
• To make output easier to understand, we should also
print out the job titles:
– Select Title, count(Salary), avg(Salary) from Employee
group by title;
• We can even subtotal by 2 fields: What would this
command mean?
– Select Location, Title, count(Salary) from Employee
group by Location, Title;
Order by
• This clause is used for sorting.
• Default order is ascending.
• select * from Employee order by Last;
• select * from Employee order by Location, Last;
• select * from Employee where Salary > 50000
order by Location, Title;
More on “where”
• Boolean conditions: when you use the “where” clause
can include the word “and” or “or” to make complex
conditions.
– Ex. What if we wanted salaries of employees with names
starting with M or P.
• Use “in” when you want to select among several possible
values. Has the same effect as “or”
– Select * from Employee where Location in (“Dublin”, “Chicago”);
• Use “between” for an (inclusive) range of values to check
– Select * from Employee where Salary between 60000 and
70000;
Relational Database
• Databases with just 1 table are not very powerful.
• More interesting if 2 tables are related.
– Books and publishers
– Customers and orders
– Pets and owners
• Typically we have a “one-to-many” relationship
• The two tables need to have a field in common.
– You can see this if you try to list the necessary fields in the
above examples.
• In SQL, to refer to a field within some table, we use the
dot notation: Customer.First, Pet.Name, Order.ID