1. Server-Side Application and Data Management IT IS 3105 (FALL 2009)
Introduction to Databases (Cont.)
Mohamed Shehab
Lecture 5

2. Create Table
An SQL relation is defined using the CREATE TABLE command:
Create table [tablename] (A1 T1,A2 T2, … An Tn,
(integrity-constraint1), …,
(integrity-constraintk))
Each Ai is an attribute name in the table
Each Ti is the data type of values for Ai
Example
Create table students
(SID char(9) not null,
name varchar(30),
age integer,
dept varchar(20),
primary key (SID) );

3. Drop and Alter Table
The DROP TABLE command deletes all information about the dropped relation from the database
The ALTER TABLE command is used to add attributes to or remove attributes from an existing relation (table):
alter table tablename actions
where actions can be one of following actions:
ADD Attribute
DROP Attribute
ADD PRIMARY KEY (Attribute_name1,…)
DROP PRIMARY KEY

4. Insert into a Table Add a new tuple to a table: Example:
insert into table name values(V1, V2, V3);
insert into table name (C1, C2, C3) values(V1, V2, V3);
Example:
insert into students values ( , ‘Bob’, 25, SIS);
insert into students (SID, name, age, dept) values ( , ‘Bob’, 25, SIS);
Inserting multiple tuples:
insert into table name (C1, C2, C3) values(V1, V2, V3), (V1, V2, V3), (V1, V2, V3);
Example
insert into students (SID, name, age, dept) values ( , ‘Bob’, 25, SIS), ( , ‘Alice’, 20, CS);

5. Writing Database Queries
A typical SQL query has the form:
select A1, A2, …, An
from table1, table2, …, tablem
where P
Ai represents an attribute
tablei represents a table
P is a constraints (condition)
Example
select SID, name from student where dept=‘SIS’;

6. SQL Query Basic form: SELECT attributes
FROM relations (possibly multiple, joined)
WHERE conditions (selections)

7. Simple SQL Query SELECT * FROM Product WHERE category=‘Gadgets’
PName
Price
Category
Manufacturer
Gizmo
$19.99
Gadgets
GizmoWorks
Powergizmo
$29.99
SingleTouch
$149.99
Photography
Canon
MultiTouch
$203.99
Household
Hitachi
SELECT * FROM Product WHERE category=‘Gadgets’
PName
Price
Category
Manufacturer
Gizmo
$19.99
Gadgets
GizmoWorks
Powergizmo
$29.99
“selection”

8. Simple SQL Query
Product
PName
Price
Category
Manufacturer
Gizmo
$19.99
Gadgets
GizmoWorks
Powergizmo
$29.99
SingleTouch
$149.99
Photography
Canon
MultiTouch
$203.99
Household
Hitachi
SELECT PName, Price, Manufacturer FROM Product WHERE Price > 100
PName
Price
Manufacturer
SingleTouch
$149.99
Canon
MultiTouch
$203.99
Hitachi
“selection” and
“projection”

9. A Notation for SQL Queries
Input Schema
Product(PName, Price, Category, Manfacturer)
SELECT Name, Price, Manufacturer FROM Product WHERE Price > 100
Answer(PName, Price, Manfacturer)
Output Schema

10. Selections What goes in the WHERE clause:
x = y, x < y, x <= y, etc
For number, they have the usual meanings
For CHAR and VARCHAR: lexicographic ordering
Expected conversion between CHAR and VARCHAR
For dates and times, what you expect...
Pattern matching on strings: s LIKE p (next)

11. The LIKE operator s LIKE p: pattern matching on strings
p may contain two special symbols:
% = any sequence of characters
_ = any single character
Product(Name, Price, Category, Manufacturer)
Find all products whose name mentions ‘gizmo’:
SELECT * FROM Products WHERE PName LIKE ‘%gizmo%’

12. Eliminating Duplicates
Category
Gadgets
Photography
Household
SELECT DISTINCT category
FROM Product
Compare to:
Category
Gadgets
Photography
Household
SELECT category
FROM Product

13. Ordering the Results
SELECT pname, price, manufacturer
FROM Product
WHERE category=‘gizmo’ AND price > 50
ORDER BY price, pname
Ordering is ascending, unless you specify the DESC keyword.
Ties are broken by the second attribute on the ORDER BY list, etc.

14. Joins in SQL Connect two or more tables: What is the Connection
PName
Price
Category
Manufacturer
Gizmo
$19.99
Gadgets
GizmoWorks
Powergizmo
$29.99
SingleTouch
$149.99
Photography
Canon
MultiTouch
$203.99
Household
Hitachi
Product
Company
CName
StockPrice
Country
GizmoWorks 25
USA
Canon 65
Japan
Hitachi 15
What is
the Connection
between
them ?

15. Join between Product and Company
Joins
Product (pname, price, category, manufacturer)
Company (cname, stockPrice, country)
Find all products under $200 manufactured in Japan; return their names and prices.
Join between Product and Company
SELECT PName, Price FROM Product, Company WHERE Manufacturer=CName AND Country=‘Japan’ AND Price <= 200

16. Joins in SQL
Product
Company
PName
Price
Category
Manufacturer
Gizmo
$19.99
Gadgets
GizmoWorks
Powergizmo
$29.99
SingleTouch
$149.99
Photography
Canon
MultiTouch
$203.99
Household
Hitachi
Cname
StockPrice
Country
GizmoWorks 25
USA
Canon 65
Japan
Hitachi 15
SELECT PName, Price FROM Product, Company WHERE Manufacturer=CName AND Country=‘Japan’ AND Price <= 200
PName
Price
SingleTouch
$149.99

17. Joins Product (pname, price, category, manufacturer)
Purchase (buyer, seller, store, product)
Person(persname, phoneNumber, city)
Find names of people living in Seattle that bought some product in the ‘Gadgets’ category, and the names of the stores they bought such product from
SELECT DISTINCT persname, store FROM Person, Purchase, Product WHERE persname=buyer AND product = pname AND city=‘Seattle’ AND category=‘Gadgets’

18. Disambiguating Attributes
Sometimes two relations have the same attr: Person(pname, address, worksfor) Company(cname, address)
Which address ?
SELECT DISTINCT pname, address FROM Person, Company WHERE worksfor = cname
SELECT DISTINCT Person.pname, Company.address FROM Person, Company WHERE Person.worksfor = Company.cname

19. Tuple Variables Product (pname, price, category, manufacturer)
Purchase (buyer, seller, store, product)
Person(persname, phoneNumber, city)
Find all stores that sold at least one product that the store ‘BestBuy’ also sold:
SELECT DISTINCT x.store
FROM Purchase AS x, Purchase AS y
WHERE x.product = y.product AND y.store = ‘BestBuy’
Answer (store)

20. Aliases for Columns and Tables
SELECT col1 alias1, col2 alias2 from tablename;
Example:
SELECT SID id, name nm, age, dept dno from students;
SELECT col1, col2 from tablename AS alias1;
SELECT SID, name from students as t1;

21. Aggregate Functions
Aggregate functions operate on the multiset of values of a attribute and return a value
avg(attribute): average value
min(attribute): minimum value
max(attribute): maximum value
sum(attribute): sum of values
count(attribute): number of values
To obtain the value when duplicates are removed, insert the keyword distinct before attribute name:
avg(distinct attribute)

22. Aggregate Functions A complete list is available at:

23. Modifying the Database
Three cases:
Add a tuple
INSERT INTO table_name VALUES (Val1, Val2, … , Valn)
Change tuples
UPDATE table_name
SET A1=val1, A2=val2, …, An=valn
WHERE tuple_selection_predicate
Remove tuples
DELETE FROM table_name

24. UPDATE Set all department to ‘computer science’
update student set dept=‘computer science’
In table student(SID, name, age, dept), increase the age of everyone by 1.
update student set age=age+1
In table student, update the department for the user with SID ‘ ’ to ‘CS’
Update student set dept=‘CS’ where SID=

25. DELETION Delete records of all students in the university
delete from student
Delete the students who study computer science
where dept=‘CS’