BTEC- HND In Computing-Creating Table_Week6.pptx

BTEC- HND In Computing
Module Name: Database Design & Development
Unit Number: 4
Week 7
Creating Tables
1
HND-Database Design & Development

Unit Learning Outcomes
• LO1. Use an appropriate design tool to design a relational
database system for a substantial problem.
• LO2. Develop a fully functional relational database system,
based on an existing system design.
• LO3. Test the system against user and system requirements.
• LO4. Produce technical and user documentation.
HND-Database Design & Development 2

Objectives
BE ABLE TO IDENTIFY:
• The basic concepts and principles of SQL
• The different components of SQL
• How to use SQL (DDL) to perform basic create
operations
o Create
o Insert
o Modify
o Delete data
How to use SQL(DML) to perform basic database queries

Relational Tables Can Answer
Many Queries
Student Enrolment Course
•How many courses are there & what are their names?
• Which students are enrolled for Java?
• How many students take 3 or more courses?

SQL - Structured Query
Language
• SQL was developed at IBM around 1975...
• SQL is a declarative language - says what not how
• SQL is a powerful language,
• SQL is an abstract & portable interface to RDMBs

Structured Query Language
(contd.)
3 COMPONENETS
o Data Definition Language (DDL) for creating a DB
o Data Control Language (DCL) for administering a
DB
o Data Manipulation Language (DML) to insert,
delete and modify data in a table

SQL Syntax
SQL uses English keywords & user-defined names
CREATE TABLE Staff (
StaffNo INTEGER,
Salary FLOAT,
Lname CHAR(20)
);
INSERT INTO Staff VALUES (32, 25000.0, 'Smith');
By convention, keywords are upper-case
Text data is enclosed using single quotes (‘ ' ‘)
Round brackets (‘(‘) are used to group related items
Commas (‘,’) separate items in a list
Statements are terminated with a semicolon (‘;’)

SQL Terminology
SQL does not use formal relational terminology
Formal Informal (SQL)
Relation Table
Tuple Row
Attribute Column
Cardinality No. of rows
Degree No. of columns
Relationships Foreign keys
Constraints Assertions

(contd.)
• Creating tables…
o Tables can be created using CREATE TABLE
statement
o There are different data types available in SQL2

(contd.)
• Integer (INT, INTEGER & SMALLINT)
• Real numbers (FLOAT, REAL, DOUBLE)
• Formatted numbers DECIMAL(i,j) or DEC(i,j) or NUMERIC(i,j)
• Character strings
o Fixed length: CHAR(n) or CHARACTER(n)
o Variable length: VARCHAR(n)
• Date and Time: DATE and TIME data types are supported in
SQL2

(contd.)
Example
CREATE TABLE Student (
name CHAR(20),
address CHAR(25),
age INTEGER,
gpa REAL
);

(contd.)
• Primary Key constraint
o PRIMARY KEY
stdid CHAR (10) PRIMARY KEY,
name CHAR(20),
address CHAR(25),
age INTEGER,
gpa REAL
);

(contd.)
Alternative:
stdid CHAR (10),
name CHAR(20),
address CHAR(25),
age INTEGER,
gpa REAL,
PRIMARY KEY (stid)
);

(contd.)
• Other candidate keys…
o UNIQUE - identifies an individual tuple uniquely in a relation or table. A table
can have more than one unique key unlike primary key. Unique key constraints
can accept only one NULL value for column.
Stdid CHAR (10) PRIMARY KEY
Name CHAR(20),
Address CHAR(25),
Age INTEGER,
Gpa REAL,
NIC CHAR(10) UNIQUE);

(contd.)
• Referential Integrity Constraints
o FOREIGN KEY………REFERENCES
• Student (stdId, name ,address , age , gpa)
• Grade( subjectId, stdId , grade)
CREATE TABLE Grade
(
subjectId CHAR(4),
stdId CHAR(10),
grade CHAR(2),
PRIMARY KEY(subjectId, stdId),
FOREIGN KEY(stdId) REFERENCES Student
)

(contd.)
• Alternative
o FOREIGN KEY
CREATE TABLE Grade (
subjectId CHAR(4),
stdId CHAR(10) REFERENCES Student(stdId),
grade CHAR(2),
PRIMARY KEY(subjectId,stdid)
);

(contd.)
• The use of a constraint name allows identification of a
constraint which can be dropped later (using the ALTER
TABLE command)
CREATE TABLE Grade (
subjectId CHAR(4),
stdId CHAR(10) ,
grade CHAR(2),
PRIMARY KEY(subjectId,stdid),
CONSTRAINT fk_Grade FOREIGN KEY(stdid)
REFERENCES Student(stdId)
);

(contd.)
• Specifying NOT NULL constraints…
o NOT NULL
Name CHAR(20) NOT NULL,
Address CHAR(25),
Age INTEGER,
Gpa REAL
);

(contd.)
• Specifying default values…
o DEFAULT - is used to set a default value for a column.
o The default value will be added to all new records, if no other value is specified.
Name CHAR(20),
Address CHAR(25) DEFAULT ‘Malabe’,
Age INTEGER,
Gpa REAL
);

(contd.)
• Specifying valid values…
o CHECK constraints - is used to limit the value range that can be placed in a
column.
CREATE TABLE Emp (
….
age INT CHECK (age BETWEEN 0 AND 120),
….);

(contd.)
• Referential Triggered Action:
o Operations
• ON UPDATE
• ON DELETE
o Actions
• SET NULL
• CASCADE
• SET DEFAULT

(contd.)
ON DELETE CASCADE
• It specifies that the child data is deleted when the
parent data is deleted.
ON UPDATE
• Optional. It specifies what to do with the child data
when the parent data is updated. You have the options of
NO ACTION, CASCADE, SET NULL, or SET DEFAULT.

(contd.)
NO ACTION
• It is used in conjunction with ON DELETE or ON
UPDATE. It means that no action is performed with the
child data when the parent data is deleted or updated.
Cascade
UPDATE. It means that the child data is either deleted or
updated when the parent data is deleted or updated.

(contd.)
SET NULL
UPDATE. It means that the child data is set to NULL
when the parent data is deleted or updated.
SET DEFAULT
UPDATE. It means that the child data is set to their
default values when the parent data is deleted or
updated.

(contd.)
CREATE TABLE Employee (
NIC VARCHAR(10) PRIMARY KEY,
name VARCHAR(50) UNIQUE NOT NULL,
address VARCHAR(25) DEFAULT 'Colombo',
works_in INTEGER,
CONSTRAINT fk_EmpDept FOREIGN KEY (works_in)
REFERENCES Dept ON DELETE CASCADE
ON UPDATE NO ACTION
);

(contd.)
• Dropping tables
DROP TABLE Employee [RESTRICT|CASCADE]
o RESTRICT drops if no other constraints (such as foreign
keys or views exist)
o CASCADE drops all constraints & views that reference it
* SQL Server 2000 has only RESTRICT option which is the
default

(contd.)
• Altering tables…
o ALTER TABLE can be used to add or drop a column,
change a column definition, and adding or dropping
table constraints
The new column has null values. Hence, NOT NULL
cannot be used here
ALTER TABLE Employee ADD Job VARCHAR(12)

(contd.)
Dropping a column…
Changing column definition…
Dropping a constraint
ALTER TABLE Employee DROP COLUMN Job
ALTER TABLE Employee ALTER COLUMN job vachar(50)
ALTER TABLE Employee DROP fk_EmpDept

(contd.)
• We can modify data using the following three commands:
INSERT, DELETE and UPDATE
• INSERT statement:
o Inserting a single row
• *The order of values must be the same as in the
CREATE TABLE statement
INSERT INTO Dept VALUES (1, 'Sales', 'BoC Merchant Tower')

(contd.)
Inserting to user-specified columns
• * Only the columns are specified are filled with values.
Unspecified columns are filled with NULL if there is no
default values.
INSERT INTO Employee (NIC, name, works_in)
VALUES ('781111111V', 'Ajith Perera', 1)

(contd.)
• Inserting multiple rows…
INSERT INTO Employees
<Select statement>*
*we’ll learn the select statement in detail later

(contd.)
• Deleting tuples from tables…
o Deleting all records
o Deleting only specified records
DELETE FROM <table>
WHERE <selection-condition>
o Completely removing a table is a DDL operation
DELETE FROM Dept
DELETE FROM Dept WHERE dno = 2
DROP TABLE Staff

(contd.)
• Updating tuples in a table
UPDATE <table>
SET <column> = <expression>
WHERE <selection condition>

(contd.)
• Updating all tuples
• Updating selected tuples
UPDATE Employee
SET works_in = 2
WHERE NIC = ‘781111111V’
UPDATE Employee SET works_in = 1

Exercises…
• Consider the following schema:
Student(StudentNo:Integer; name:varchar(50),
major:char(4); GPA:float)
Write SQL statements to perform the following
1. Create the above table
2. Insert the following information:
StudentNo Name Major GPA
1 Sampath EE 3.5
2 Nishani CSE 34

Exercises… (contd.)
3. Update Sampath’s GPA to 3.7.
4. Delete student table
5. Add a column address (i.e. address: varchar(50) ) to the
Student table.
6. Change the data type of address column into varchar(100).
7. Add a checking rule to GPA column, GPA values should
between 0 and 4.
8. Remove the check constraint added to the GPA column.
9. Create table Major(majorId , description).
10. Change student table to reflect Primary Key.

Summary
• SQL is the standard query language for RDBMS
• Three main categories of SQL
o DDL, Data Definition Language
o DCL, Data Control Language
o DML, Data Manipulation Language
• CREATE belongs to DDL

Next Lecture
SQL ctd..

Q & A

Thank You.

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