Database Systems
Basic SQL
1
Outline

SQL Data Definition and Data Types

Specifying Constraints in SQL

Basic Retrieval Queries in SQL

INSERT, DELETE, and UPDATE Statements in
SQL

Additional Features of SQL
2
Basic SQL


SQL language
 Considered one of the major reasons for the
commercial success of relational databases
SQL
 Structured Query Language
 Statements for data definitions, queries, and
updates (both DDL and DML)
 SQL is not a programming language.
 SQL commands can be used interactively as a
query language within the DBMS or SQL
commands can be embedded within
programming languages.
3
Types of SQL Commands

Data Definition Language (DDL):
 Commands that define a database - Create,
Alter, Drop

Data Manipulation Language (DML)
 Commands that maintain and query a
database.

Each statement in SQL ends with a semicolon
4
SQL Concept & Relational Concept

Terminology:
 Table, row, and column used for relational
model terms relation, tuple, and attribute
SQL Concept
Relational Concept
Table
Relation
Row
Tuple
Column
Attribute
5
The CREATE TABLE Command

CREATE statement
 Main SQL command for data definition
 Specify a new relation
 Provide name
 Specify attributes and initial constraints

Base tables (base relations)
 Relation and its tuples are actually created
and stored as a file by the DBMS
6
The CREATE TABLE Command

Can optionally specify schema:

CREATE TABLE COMPANY.EMPLOYEE ...
or



CREATE TABLE EMPLOYEE ...
Create the following relation:
 Student(SSN, Name, GPA, Age).
SQL> create table Student (
2 SSN
char(9) not null,
3 Name
varchar(20),
4 GPA
number(3,2),
5 Age
number(2),
6 primary key (SSN));
7
8
9
Attribute Data Types

char(n)
fixed length character string of length n

varchar(n)
variable length characters of length up to n

number(n)
integer and real values of up to n digits

number
integer and real values of up to 40 digits

integer(n)
integer of up to n digits

intege r
integer of up to 40 digits

date
yyyy-mm-dd (10 positions)

time
typically in the form HH:MM:SS
10
Domain Definitions


CREATE DOMAIN <name> As <data-type>;
 CREATE DOMAIN SSN-TYPE AS CHAR(9);

We can use SSN_TYPE in place of CHAR(9)

This style in writing SQL statements is preferred as it
makes it easier to change the data types of attributes.
A domain can also have an optional default specification
via default clause.
 CREATE DOMAIN DNO-DOM AS CHAR(2)
DEFAULT 01;
11
Specifying Constraints in SQL

Constraints are rules or regulations imposed on
data to ensure their integrity and correctness.

Constraints on individual columns.

Constraints on a table.

Constraints on multiple tables.
12
Constraints on Columns (1)
Create table Book(
ISBN char(15) primary key,
Title varchar(50) unique,
Price number(5,2) check (Price>0),
Edition number(2) default 1
check (Edition > 0),
Publisher_name varchar(30)
references Publisher(Name));
13
Constraints on Individual Columns (2)



type
values must be of the given type
not null no null value can be taken
unique
 Specifies alternate (secondary) keys
 Dname VARCHAR(15) UNIQUE;
no identical non-null values
primary key
 Specifies one or more attributes that make up the
primary key of a relation
 no null value and no identical values


 Dnumber INT PRIMARY KEY;

check constraint definition
 values must satisfy the check condition.
 Dnumber INT NOT NULL CHECK (Dnumber > 0 AND
Dnumber < 21);
14
Constraints on Individual Columns (3)

Syntax for column definition:
col_name data_type [default value] [constraints]

Syntax for column constraints:
[constraint constraint_name]
[not] null | check condition |
unique | primary key |
references table_name [(column)]
[on delete cascade] [on update cascade]
15
Create Table Example (4)
Create table Enrollment(
SSN char(9) references Students,
Crs_no varchar(7)
not null,
Section_no number(2)
not null,
Grade char,
primary key(SSN,Crs_no,Section_no),
foreign key (Crs_no,Section_no)
references Section);
16
Giving Names to Constraints


Syntax for table constraints:
[constraint constraint_name]
check condition |
unique (column {, column}) |
primary key (column {, column}) |
foreign key (column {, column})
references table_name[(column{,
column)]
CHECK clauses at the end of a CREATE TABLE
statement
 Apply to each tuple individually

CHECK (Dept_create_date <= Mgr_start_date);
17
Giving Names to Constraints
Create table Graduate(
SSN char(9) primary key,
Name varchar(30),
Address varchar(80),
Degree varchar(8) check (Degree in
{‘Bachelor’, ‘Master’, ‘Ph.D.’}),
GPA number (3,2) not null,
unique (Name, Address),
constraint ic12 check (GPA>=2.0 and
(Degree=‘Bachelor’ or GPA>=3.0)));
18
Basic Retrieval Queries in SQL

SELECT statement
 One basic statement for retrieving information
from a database
20
The SELECT-FROM-WHERE

Basic form of the SELECT statement:
21
The SELECT-FROM-WHERE Structure

Logical comparison operators
 =, <, <=, >, >=, and <>

Projection attributes
 Attributes whose values are to be retrieved

Selection condition
 Boolean condition that must be true for any
retrieved tuple
22
23
24
The SELECT-FROM-WHERE

Find the SSN, Name and GPA of all students whose GPA is
higher than 3.8.
Select SSN, Name, GPA
From Students
Where GPA > 3.8;

Select all EMPLOYEE SSNs.
SELECT SSN
FROM EMPLOYEE;

Select all combinations of Employee SSNs and
Department Dname.
SELECT SSN, DNAME
FROM EMPLOYEE, DEPARTMENT;
25
The SELECT-FROM-WHERE

Select all attributes of employees who work for
department number 5;
SELECT * FROM EMPLOYEE
WHERE DNO = 5;

Find the names and GPAs of all students who take
database systems.
Select Name, GPA
From Student, Enrollment, Course
Where Title = `database systems` and
Students.SSN = Enrollment.SSN and
Enrollment.Course_no=Courses.Course_no;
26
Ambiguous Attribute Names

Same name can be used for two (or more)
attributes
 As long as the attributes are in different
relations
 Must qualify the attribute name with the
relation name to prevent ambiguity
EMPLOYEE(SSN, Name, …., DNo)
DEPARTMENT(DNo, Name, …)
27
Aliasing, Renaming, and Tuple Variables

Aliases or tuple variables
 Declare alternative relation names E and S
 EMPLOYEE AS E(Fn, Mi, Ln, Ssn,
Bd, Addr, Sex, Sal, Sssn, Dno)
28
Dealing with Aliasing (1)

For each employee retrieve the employee’s first and
last name and the first and last name of his or her
immediate advisor.
SELECT E.Fname, E.Lname, S.Fname, S.Lname
FROM Employee E, Employee S
WHERE E.SuperSSN = S.SSN;

We may write Employee AS E

Note that aliases can be used to shorten queries by
giving short names to relations.
29
Dealing with Aliasing (2)





We may alias attributes as well.
Employee(Name, Address, Supervisor, Dept)
Q1:
 Select NA, Adr, S, Dept
FROM EMPLOYEE AS E(NA, Adr, S, D)
Or this
 Select Name NA, Address adr, Supervisor
S, Dept D
FROM EMPLOYEE;
Find the names and GPAs of all students who take database systems.
Select Name, GPA
From Student S, Enrollment E, Course C
Where Title=`database systems‘ and S.SSN=E.SSN
and E.Course_no=C.Course_no
30
Dealing with Aliasing (3)

Find all pairs of students who have the same
GPA.
select s1.SSN, s2.SSN
from Student s1, Student s2
where s1.GPA=s2.GPA and
s1.SSN<s2.SSN;

Question:

Why use “s1.SSN < s2.SSN”?
31
Dealing with Aliasing (4)

Find the names of all students whose GPA is
higher than Tom's GPA.
select s1.Name
from Students s1, Students s2
where s2.Name=‘Tom’ and
s1.GPA>s2.GPA;
32
Renaming SELECT Attributes


SQL allows us to rename SELECT attributes
This does not significantly change the results of
a query, but it does allow us to control the
headings of the columns displayed on reports
SELECT FNAME AS FN, LNAME AS LN
FROM EMPLOYEE
WHERE SUPERSSN IS NULL

The same tuples will be selected as for the last
query, but now the columns will be labeled FN
and LN instead of FNAME and LNAME.
33
Unspecified WHERE Clause
and Use of the Asterisk


Missing WHERE clause
 Indicates no condition on tuple selection
CROSS PRODUCT
 All possible tuple combinations
34
Unspecified WHERE Clause
and Use of the Asterisk (cont’d.)

Specify an asterisk (*)
 Retrieve all the attribute values of the selected
tuples
35
Unspecified Where Clause & Use of
Asterisk




To retrieve all attributes of a relation, use the shorthand *
To retrieve all the attribute values of the selected tuples, a * is
used, which stands for all the attributes
Find all students whose GPA is higher than 3.8.
select * from Students where GPA > 3.8;
The where-clause may be absent.
 Find the Names of all students.
select Name from Students;
 Select all EMPLOYEE SSNs.
SELECT SSN FROM EMPLOYEE;
36
Unspecified Where clause

A missing WHERE-clause indicates no condition;
hence, all tuples of the relations in the FROM-clause are
selected

This is equivalent to the condition WHERE TRUE

Retrieve the SSN values for all employees.
SELECT
SSN FROM EMPLOYEE;

If more than one relation is specified in the FROM-clause
and there is no join condition, then the CARTESIAN
PRODUCT of tuples is selected
37
Use of Asterisk

Retrieve all the attributes of an employee and the
attributes of the department he/she works in for every
employee of the “Research” department.
SELECT * FROM Employee, Department
WHERE Dname = “Research” AND DNO =
Dnumber;

Specify (retrieve) the cross product of the Employee and
Department relations;
SELECT * FROM Employee, Department;
Select all combinations of Employee SSNs and
Department Dname.
SELECT SSN, DNAME FROM EMPLOYEE,
DEPARTMENT;

38
Tables as Sets in SQL






SQL does not automatically eliminate duplicate tuples in query
results
Use the keyword DISTINCT in the SELECT clause
 Only distinct tuples should remain in the result
Find the Names of all students without duplicate rows.
Select distinct Name from Student;
Select all can be used to explicitly request that all
duplicate rows are kept.
Is the following query an efficient query?
select distinct SSN, Name from Student
Retrieve the salary for every employee.
 duplicates may appear
SELECT Salary FROM Employee;
 duplicates will be eliminated
SELECT DISTINCT Salary FROM Employee;
39
Tables as Sets in SQL (cont’d.)

Set operations
 UNION, EXCEPT (difference), INTERSECT
 Corresponding multiset operations: UNION ALL,
EXCEPT ALL, INTERSECT ALL)
 union removes duplicate rows.
 union all keeps duplicate rows.
40
Substring Pattern Matching and
Arithmetic Operators



LIKE comparison operator
 Used for string pattern matching
 % replaces an arbitrary number of zero or more
characters
 underscore (_) replaces a single character
Standard arithmetic operators:
 Addition (+), subtraction (–), multiplication
(*), and division (/)
BETWEEN comparison operator
41
Substring Pattern Matching

Find the course numbers and titles of all
courses whose title contains “systems”.
select Course_no, Title
from Courses
where Title like `%systems%`;

% matches 0 or more characters.
42
Substring Pattern Matching

Find all students whose name starts with M and
is six-character long.
select * from Students
where Name like `M_ _ _ _ _`;

_ matches exactly one character
not like is the opposite of like.


Find all students whose name contains a _.
select * from Students
where Name like `%\_ %`;
43
Substring Pattern Matching

Retrieve all employees whose address in
Housten, Texas.
SELECT Fname, Lname
FROM Employee
WHERE Address LIKE ’%Houston, TX%’;

Find all employees who were born during the
1950s.
SELECT Fname, Lname
FROM Employee
WHERE Bdate LIKE ’195_ _ _ _
_’;
44
Arithmetic Operators

Show resulting salaries if every employee working on the
‘productX’ project is given a 10% raise.
SELECT Fname, Lname, 1.1*Salary
FROM Employee, Works_on, Project
WHERE SSN = ESSN AND PNO = Pnumber
AND
Pname=“ProductX”;

Find the names of all students whose GPA is between 3.5
and 3.8, inclusive.
select Name from Students
where GPA between 3.5 and 3.8;

not between ... and … is the opposite of between … and
...
45
Arithmetic Operators

Employees (SSN, Name, Salary)

Find the SSN, name and annual salary of each
employee.
select SSN, Name, 12*Salary
from Employees;
or
select SSN, Name,12*Salary as Annual_Salary
from Employees;
46
Ordering of Query Results

Use ORDER BY clause
 Keyword DESC to see result in a descending
order of values
 Keyword ASC to specify ascending order
explicitly
 ORDER BY D.Dname DESC, E.Lname
ASC, E.Fname ASC
47
Ordering Tuples

Find the names of all students and order the
names in ascending order.
select Name
from Students
order by Name asc;

ascending order is the default in order by clause.

We can write:
order by Dname desc, Lname ASC, Fname
ASC
48
Ordering Tuples

Find all the students whose GPA is higher than 3.5 and
order the result in descending order by GPA, and for
students having the same GPA, order them in ascending
order by their names.
select * from Students
where GPA > 3.5
order by GPA desc, Name asc;
49
Ordering Tuples

Retrieve a list of employees and the projects they are
working on, ordered by department and, within each
department, alphabetically by last name, first name;
SELECT Dname, Lname, Fname, Pname
FROM Department, Employee, Works_on, Project
WHERE Dnumber=DNO AND SSN=ESSN AND PNO=Pnumber
ORDER BY Dname, Lname, Fname;
50
Discussion and Summary
of Basic SQL Retrieval Queries
51
INSERT, DELETE, and UPDATE
Statements in SQL

Three commands used to modify the database:
 INSERT, DELETE, and UPDATE

Relation schemas under consideration:
 Student(SSN, Name, GPA, Age)
 Course(CNo, Title, DName)
 Enrollment(SSN, CNo, Grade)
52
The INSERT Command

Specify the relation name and a list of values for
the tuple
53
Insert


In its simplest form, it is used to add one or more
tuples to a relation
Attribute values should be listed in the same
order as the attributes were specified in the
CREATE TABLE command.

Syntax:
insert into table_name [(column {, column})]
[values (expression {, expression})] | [Subselect]

Multiple tuples can be inserted with the same INSERT
command, tuples are separated by commas and enclosed
between ( and ).
54
Insert



Add a new student (123, Ali, null, 22) to the
student table Student(SSN, Name, GPA, Age).
insert into Students values (`123`,`Ali`,null,22);
 Order of values should agree with the original
definition of Student.
or
insert into student(name, ssn, age)
values (`Ali`,`123`,22)
Attributes with NULL and DEFAULT values can
be left out.
55
Insert

Insert two tuples into the Students table
insert into Students values
(‘111223333’, ‘Smith’, 3.45, 23)
(‘444556666’, ‘Maria’, 3.60, 22);

Suppose table Top_Students (SSN, Name, GPA)
has been created.

Find all students whose GPA is 3.8 or higher and
save the result in the Top_Students table.
insert into Top_Students select SSN, Name,
GPA
from Student where GPA >= 3.8;
56
Insert
CREATE TABLE DEPTS-INFO(
DNAME
VARCHAR(15),
NO-OF-EMPS INTEGER,
TOTTAL-SAL INTEGER);
INSERT INTO DEPTS-INFO
(DNAME, NO-OF-EMPS, TOTAL-SAL)
SELECT DNAME, count(*), sum(SALARY)
FROM DEPARTMENT, EMPOYEE
WHERE DNUMBER = DNO
GROUP BY DNAME;
57
Inserting Null Data
INSERT INTO COURSE
COLUMN LIST IS NEEDED IF
(COURSE_CODE, CREDIT_HOURS) YOU PLAN TO LEAVE OUT A
VALUE IN THE VALUE LIST
VALUES (‘MIS499’,4);
INSERT INTO COURSE
VALUES (‘MIS499’,’’,4);
COLUMN LIST CAN BE OMITTED
IF YOU PUT IN A BLANK VALUE
THE NULL KEYWORD CAN
BE USED TO CREATE A BLANK
COLUMN
INSERT INTO COURSE
VALUES (‘MIS499’,NULL,4);
ALL OF THESE ASSUME THAT THE DATABASE ALLOWS THE COLUMN TO
BE NULL. YOU CANNOT LEAVE PRIMARY KEYS BLANK
58
Delete






Removes tuples from a relation
Includes a WHERE-clause to select the tuples to be
deleted
Tuples are deleted from only one table at a time (unless
CASCADE is specified on a referential integrity
constraint)
A missing WHERE-clause specifies that all tuples in the
relation are to be deleted; the table then becomes an
empty table
The number of tuples deleted depends on the number of
tuples in the relation that satisfy the WHERE-clause
Referential integrity should be enforced
59
Delete

Syntax:
delete from table_name
[where search_condition]

Delete all tuples from Students.
delete from Students;

The schema of Students remains.

Delete all students who take no courses.
delete from Students
where SSN not in (select SSN from
Enrollment);
60
The DELETE Command

Removes tuples from a relation
 Includes a WHERE clause to select the tuples to
be deleted
61
Delete
DELETE FROM Employee WHERE Lname =
‘Brown’;
DELETE FROM Employee where SSN =
‘123456789’
DELETE FROM EMPLOYEE
WHERE DNO IN (SELECT Dnumber FROM
Department
WHERE Dname = ‘Research’);
62
Update






Used to modify attribute values of one or more
selected tuples
A WHERE-clause selects the tuples to be
modified
An additional SET-clause specifies the
attributes to be modified and their new values
Each command modifies tuples in the same
relation
Referential integrity should be enforced
Syntax:
update table_name
set column = {expression | null}
{, column = {expression | null}}
[where search_condition]
63
Update

Increase the GPA of the student with SSN=123 by 0.5.
update Student
set GPA = GPA + 0.5
where SSN = '123';

Set the Grade of every student who takes database
systems to be A.
update Enrollment
set Grade = 'A' where CNo in
(select CNo from Course
where title='database systems');
64
Update

Change the location and controlling department
number of project number 10 to 'Bellaire' and 5,
respectively.
UPDATE Project
SET Plocation = ‘Bellaire’, Dnum = 5
WHERE Pnumber=10;

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’);
65
The UPDATE Command


Modify attribute values of one or more selected
tuples
Additional SET clause in the UPDATE command
 Specifies attributes to be modified and new
values
66