1. Database technology Lecture 2: Relational databases and SQL
Jose M. Peña

2. Database design process

3. Relational model concepts
Attributes
...
EMPLOYEE
FNAME M
LNAME
SSN
BDATE
ADDRESS S
SALARY
SUPERSSN
DNO
Ramesh K
Narayan …
38000 5
Joyce A
English F
25000
Ahmad V
Jabbar 4
James E
Borg
55000
null 1
Tuples
...
Relation: Set of tuples, i.e. no duplicates are allowed.
Database: Collection of relations.
EMPLOYEE ( FNAME, M, LNAME, SSN, BDATE, ADDRESS, S, SALARY, SUPERSSN, DNO)
Relation schema 3

4. Relational model concepts
Domain
String shorter than 30 chars
Integer
400 < x < 8000
Character
M or F
yyyy-mm-dd
EMPLOYEE
FNAME M
LNAME
SSN
BDATE
ADDRESS S
SALARY
SUPERSSN
DNO
Ramesh K
Narayan …
38000 5
Joyce
Null
English F
Ahmad V
Jabbar
25000 4
James
Borg
55000 1
NULL value 4

5. Relational model constraints
EMPLOYEE
FNAME M
LNAME
SSN
BDATE
ADDRESS S
SALARY
SUPERSSN
DNO
Ramesh K
Narayan …
38000 5
Joyce
Null
English F
Ahmad V
Jabbar
25000 4
James
Borg
55000 1
Entity integrity constraint 5

6. Relational model constraints
Foreign keys
EMPLOYEE
FNAME M
LNAME
SSN
BDATE
ADDRESS S
SALARY
SUPERSSN
DNO
Ramesh K
Narayan …
38000 5
Joyce A
English F
25000
Ahmad V
Jabbar 4
James E
Borg
55000
Null 1
Referential integrity constraint
DEPARTMENT
DNAME
DNUMBER
MGRSSN
MGRSTARTDATE
Research 5
Administration 4
Headquarters 1 6

7. Relational model constraints
(Atomic) domain (or NULL).
Key.
Entity integrity: A PK cannot take NULL values.
Referential integrity: A FK in a relation can only refer to the PK of another relation, and the domains of the FK and PK must coincide, and the FK takes NULL value or values that exist for the PK. 7

8. SQL Used in many DBMSs. Declarative (what data to get, not how).
relational data model SQL
relation table
attribute column
tuple row
Used in many DBMSs.
Declarative (what data to get, not how).
DDL (Data Definition Language)
CREATE, ALTER, DROP
Queries
SELECT
DML (Data Manipulation Language)
INSERT, DELETE, UPDATE … 8

9. COMPANY schema
EMPLOYEE (FNAME, MINIT, LNAME, SSN, BDATE, ADDRESS, SEX, SALARY, SUPERSSN, DNO)
DEPT_LOCATIONS (DNUMBER, DLOCATION)
DEPARTMENT (DNAME, DNUMBER, MGRSSN, MGRSTARTDATE)
WORKS_ON (ESSN, PNO, HOURS)
PROJECT (PNAME, PNUMBER, PLOCATION, DNUM)
DEPENDENT (ESSN, DEPENDENT-NAME, SEX, BDATE, RELATIONSHIP) 9

10. Create tables CREATE TABLE <tablename> (
<colname> <datatype> [<constraint>], …,
[<constraint>], … );
Data types: Integer, decimal, number, varchar,char, etc.
Constraints: Not null, primary key, foreign key, unique, etc. 10

11. Create tables CREATE TABLE WORKS_ON ( ESSN integer, PNO integer,
HOURS decimal(3,1),
constraint pk_workson
primary key (ESSN, PNO),
constraint fk_works_emp
FOREIGN KEY (ESSN) references EMPLOYEE(SSN),
constraint fk_works_proj
FOREIGN KEY (PNO) references PROJECT(PNUMBER) ); 11

12. Modify tables Delete a table and its definition
Change the definition of a table: Add, delete and modify columns and constraints.
ALTER TABLE EMPLOYEE ADD JOB VARCHAR(12);
ALTER TABLE EMPLOYEE DROP COLUMN ADDRESS CASCADE;
ALTER TABLE WORKS_ON DROP FOREIGN KEY fk_works_emp;
ALTER TABLE WORKS_ON ADD CONSTRAINT fk_works_emp
FOREIGN KEY (ESSN) REFERENCES EMPLOYEE(SSN);
Delete a table and its definition
DROP TABLE EMPLOYEE; 12

13. Query tables SELECT <attribute-list> FROM <table-list>
WHERE <condition>;
Attribute list: A1, …, Ar
Attributes whose values are required.
Table list: R1, …, Rk Relations to be queried
Condition: Boolean expression
It identifies the tuples that should be retrieved. It may include comparison operators(=, <>, >, >=, etc.) and/or logical operators (and, or, not). 13

14. Simple query List the SSN for all employees. SELECT SSN SELECT FROM
SELECT SSN
SELECT
FROM
FROM EMPLOYEE; 14

15. Use of * List all information about the employees of department 5.
SELECT
FROM
WHERE
SELECT FNAME, MINIT, LNAME,SSN, BDATE, ADDRESS, SEX, SALARY, SUPERSSN, DNO
FROM EMPLOYEE
WHERE DNO = 5; or
Comparison operators
{=, <>, >, =>, etc.}
SELECT *
FROM EMPLOYEE
WHERE DNO = 5; 15

16. Simple query
List the last name, birth date and address for all employees whose name is `Alicia J. Zelaya‘.
SELECT
FROM EMPLOYEE
WHERE
LNAME, BDATE, ADDRESS
FNAME = ‘Alicia’
AND MINIT = ‘J’
AND LNAME = ‘Zelaya’;
Logical operators
{and, or, not}
LNAME BDATE ADDRESS
Zelaya Castle, Spring, TX 16

17. Pattern matching
List the birth date and address for all employees whose last name contains the substring ‘aya’.
SELECT BDATE, ADDRESS
FROM EMPLOYEE
WHERE LNAME LIKE ‘%aya%’;
LIKE comparison operator
% replaces 0 or more characters
_ replaces a single character
LNAME BDATE ADDRESS
Zelaya Castle, Spring, TX
Narayan Fire Oak, Humble, TX 17

18. Tables as sets List all salaries. SELECT SALARY FROM EMPLOYEE; SALARY
30000
40000
25000
43000
38000
55000
List all salaries.
SELECT SALARY
FROM EMPLOYEE; 18

19. Tables as sets
SQL considers a table as a multi-set (bag), i.e. tuples can occur more than once in a table. This is different in a relational model.
Why?
Removing duplicates is expensive.
User may want information about duplicates.
Aggregation operators. 19

20. Example List all salaries. SELECT SALARY FROM EMPLOYEE;
30000
40000
25000
43000
38000
55000
List all salaries.
SELECT SALARY
FROM EMPLOYEE;
SALARY
30000
40000
25000
43000
38000
55000
List all salaries without duplicates.
SELECT DISTINCT SALARY
FROM EMPLOYEE; 20

21. Set operations
Duplicate tuples are removed.
Queries can be combined by set operations: UNION, INTERSECT, EXCEPT (MySQL only supports UNION)
Retrieve the first names of all people in the database.
SELECT FNAME FROM EMPLOYEE
UNION
SELECT DEPENDENT_NAME FROM DEPENDENT;
Which department managers have dependents? Show their SSN.
SELECT MGRSSN FROM DEPARTMENT
INTERSECT
SELECT ESSN FROM DEPENDENT; E D M DE 21

22. Ambiguous names: Aliasing
What if the same attribute name is used in different relations ?
No alias SELECT NAME, NAME FROM EMPLOYEE, DEPARTMENT WHERE DNO=DNUMBER;
Whole name SELECT EMPLOYEE.NAME, DEPARTMENT.NAME FROM EMPLOYEE, DEPARTMENT WHERE EMPLOYEE.DNO=DEPARTMENT.DNUMBER;
Alias SELECT E.NAME, D.NAME FROM EMPLOYEE E, DEPARTMENT D WHERE E.DNO=D.DNUMBER; 22

23. Join: Cartesian product
LNAME DNAME
Smith Research
Wong Research
Zelaya Research
Wallace Research
Narayan Research
English Research
Jabbar Research
Borg Research
Smith Administration
Wong Administration
Zelaya Administration
Wallace Administration
Narayan Administration
English Administration
Jabbar Administration
Borg Administration
Smith Headquarters
Wong Headquarters
Zelaya Headquarters
Wallace Headquarters
Narayan Headquarters
English Headquarters
Jabbar Headquarters
Borg Headquarters
List all employees and the names of
their departments.
SELECT LNAME, DNAME
FROM EMPLOYEE, DEPARTMENT;
Smith
Wong
Zelaya
Wallace
Narayan
English
Jabbar
Borg
LNAME
EMPLOYEE
DNO 5 4 1
DEPARTMENT
DNAME
DNUM
Research
Administration
headquarters 5 4 1 23

24. Join: Equijoin List all employees and the names of their departments.
LNAME DNO DNAME DNUMBER
Smith 5 Research
Wong 5 Research
Zelaya 4 Research
Wallace 4 Research
Narayan 5 Research
English 5 Research
Jabbar Research
Borg Research
Smith Administration
Wong Administration
Zelaya Administration 4
Wallace 4 Administration 4
Narayan 5 Administration
English Administration
Jabbar 4 Administration 4
Borg Administration
Smith Headquarters
Wong Headquarters
Zelaya Headquarters
Wallace 4 Headquarters
Narayan 5 Headquarters
English Headquarters
Jabbar Headquarters
Borg Headquarters
Primary key in
DEPARTMENT
Foreign key in
EMPLOYEE
Cartesian product
List all employees and the
names of their departments.
SELECT LNAME, DNAME
FROM EMPLOYEE,
DEPARTMENT
WHERE DNO = DNUMBER;
Equijoin
Thetajoin
{=, <>, >, =>, <=, !=} 24

25. Join: Self-join
List the last name for all employees together with the last names of their bosses.
SELECT E.LNAME “Employee”, S. LNAME “Boss”
FROM EMPLOYEE E, EMPLOYEE S
WHERE E.SUPERSSN = S.SSN;
Employee Boss
Smith Wong
Wong Borg
Zelaya Wallace
Wallace Borg
Narayan Wong
English Wong
Jabbar Wallace 25

26. Join: Inner join
List the last name for all employees together with the last names of their bosses.
SELECT E.LNAME “Employee”, S.LNAME “Boss”
FROM EMPLOYEE E, EMPLOYEE S
WHERE E.SUPERSSN = S.SSN;
FROM EMPLOYEE E INNER JOIN EMPLOYEE S
ON E.SUPERSSN = S.SSN; 26

27. Join: Outer join
List the last name for all employees and, if available, show the last names of their bosses.
SELECT E.LNAME “Employee”, S. LNAME “Boss”
FROM EMPLOYEE E LEFT JOIN EMPLOYEE S
ON E.SUPERSSN = S.SSN;
LEFT JOIN, RIGHT JOIN, FULL JOIN
Employee Boss
Smith Wong
Wong Borg
Zelaya Wallace
Wallace Borg
Narayan Wong
English Wong
Jabbar Wallace
Borg NULL 27

28. Joins revisited A B Cartesian product SELECT * FROM a, b;
100 A
null B
300 C D B1 B2
100 W
200 X
null Y Z
Cartesian product
SELECT * FROM a, b; A2 A1 B1 B2 A
100 W B
null C
300 D
200 X Y Z
Equijoin, natural join, inner join
SELECT * from A, B WHERE A1=B1; A2 A1 B1 B2 A
100 W
Thetajoin
SELECT * from A, B WHERE A1>B1; A2 A1 B1 B2 C
300
100 W
200 X 28

29. Outer joins revisited A B Right outer join
SELECT * FROM A RIGHT JOIN B on A1=B1; A1 A2
100 A
null B
300 C D B1 B2
100 W
200 X
null Y Z A2 A1 B1 B2 A
100 W
null
200 X Y Z
Full outer join (union of right+left)
SELECT * FROM A FULL JOIN b on A1=B1;
Left outer join
SELECT * FROM A LEFT JOIN B on A1=B1; A2 A1 B1 B2 A
100 W
null
200 X Y Z C
300 B D A2 A1 B1 B2 A
100 W C
300
null B D 29

30. Subqueries
List all employees that do not have any project assignment with more than 10 hours.
SELECT LNAME FROM EMPLOYEE, WORKS_ON WHERE SSN = ESSN AND HOURS <= 10.0;
SELECT LNAME
FROM EMPLOYEE
WHERE SSN NOT IN (SELECT ESSN FROM WORKS_ON WHERE HOURS > 10.0); Or
WHERE NOT EXISTS (SELECT * FROM WORKS_ON WHERE SSN = ESSN AND HOURS > 10.0);
{>, >=, <, <=, <>} +
{ANY, SOME, ALL}
EXISTS 30

31. Extended SELECT syntax
SELECT <attribute-list and function-list>
FROM <table-list>
[ WHERE <condition> ]
[ GROUP BY <grouping attribute-list>]
[ HAVING <group condition> ]
[ ORDER BY <attribute-list> ]; 31

32. Aggregate functions
Built-in functions: AVG(), SUM(), MIN(), MAX(), COUNT()
They appear only in SELECT and HAVING clauses.
NULL values are not considered in the computations.
List the total number of employees.
SELECT COUNT(*)
FROM EMPLOYEE; 50
100
Null 75
AVG() 32

33. Grouping
Used to apply an aggregate function to subgroups of tuples in a relation.
GROUP BY: Grouping attributes.
HAVING: Condition that a group has to satisfy.
List, for each department with more than two employees, the department number, the number of employees and the average salary.
SELECT DNO, COUNT(*), AVG(SALARY)
FROM EMPLOYEE
GROUP BY DNO
HAVING COUNT(*) > 2;
DNO COUNT(*) AVG(SALARY) 33

34. Sort query results
Show the department names and their locations in alphabetical order.
SELECT DNAME, DLOCATION
FROM DEPARTMENT D, DEPT_LOCATIONS DL
WHERE D.DNUMBER = DL.DNUMBER
ORDER BY DNAME ASC, DLOCATION DESC;
DNAME DLOCATION
Administration Stafford
Headquarters Houston
Research Sugarland
Research Houston
Research Bellaire 34

35. Null values List all employees that do not have a boss.
SELECT FNAME, LNAME
FROM EMPLOYEE
WHERE SUPERSSN IS NULL;
‘SUPERSSN = NULL’ and
‘SUPERSSN <> NULL’
will not return any matching tuples,
because NULL is incomparable to any value,
including another NULL. 35

36. Insert data
INSERT INTO <table> (<attr>,…) VALUES ( <val>, …) ;
INSERT INTO <table> (<attr>, …) <subquery> ;
Store information about how many hours an employee works for the project ’1' into WORKS_ON.
INSERT INTO WORKS_ON VALUES ( , 1, 32.5);
Integrity constraint!
Referential integrity constraint! 36

37. Update data
UPDATE <table> SET <attr> = <val> ,… WHERE <condition> ;
UPDATE <table> SET (<attr>, ….) = ( <subquery> ) WHERE <condition> ;
Give all employees in the ‘Research’ department a 10% raise in salary.
UPDATE EMPLOYEE
SET SALARY = SALARY*1.1
WHERE DNO IN (SELECT DNUMBER
FROM DEPARTMENT
WHERE DNAME = ‘Research’);
Integrity constraint!
Referential integrity constraint! 37

38. Delete data DELETE FROM <table> WHERE <condition> ;
Delete the employees having the last name ‘Borg’ from the EMPLOYEE table.
DELETE FROM EMPLOYEE
WHERE LNAME = ‘Borg’;
DEPARTMENT 1
Headquarters 4
Administration 5
Research
MGRSSN
DNUMBER
DNAME
Foreign key
EMPLOYEE
FNAME M
LNAME
SSN
Ramesh K
Narayan
Joyce A
English
Ahmad V
Jabbar
James E
Borg
ON DELETE SET NUL / DEFAULT / CASCADE ? 38
Referential integrity constraint!

39. Views
A virtual table derived from another (possibly virtual) tables, i.e. always up-to-date.
CREATE VIEW dept_view AS
SELECT DNO, COUNT(*), AVG(SALARY)
FROM EMPLOYEE
GROUP BY DNO;
Why?
Simplify query commands.
Provide data security.
Enhance programming productivity.
Update problems. 39