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SQL Structured Query Language
Implementation Lecture – 8
Database Technology Level I
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Aims
To introduce the implementation of a Physical design using SQL.
To introduce SQL Data Definition Language (DDL).
To introduce SQL Data Manipulation Language (DML).
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Implementation of a Physical Design
Database Design Language Course (courseCode, title, cost)Entity Course is converted to the following physical design. courseCode and title are set to text and indexed appropriately, cost
is set to CurrencytblCourse
Field Name Data Type Size Format Key Type Index Required
courseCode Text 8 Primary Key Yes(no duplicates) Yes
title Text 25 Yes
cost Currency Currency No
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SQL (Data Definition Language - DDL
Database Definition Commands CREATE DATABASE DROP DATABASE SHOW DATABASES CREATE TABLE ALTER TABLE
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SQL Create Table
CREATE TABLE <table name>
(
<Column Name> <Data Type> <Conditional Clauses> ,
<Column Name> <Data Type> <Conditional Clauses> ,
…..
);
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SQL Create Table
Each column definition has 3 components.
<COLUMN NAME> this the name of the attribute identified in the design.
<DATA TYPE> specified for the attribute in the Physical design. The data types available for use will depend on those appropriate for the software with which the database is to be implemented.
<CONDITIONAL CLAUSES> such as specification of Primary Keys, Indexes and Nulls.
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SQL Create Table
CREATE TABLE tblCourse (courseCode VARCHAR(8) PRIMARY KEY, title VARCHAR(25) NOT NULL, cost CURRENCY );
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Implementation of a Physical Design
StudentCourse(studentID, courseCode) FK studentID→tblStudent Update Cascade, Delete Restrict FK courseCode→tblcourse Update Cascade, Delete Restrict
Entity StudentCourse is converted to the following physical design.
This entity has a Compound Key, all elements of the compound key are identified. Both attributes are foreign keys. This means that their data type and size must exactly
match the data type and the field to which they will be linking to enforce the relationship between the tables.
Compound keys are always indexed yes (duplicates OK)
Field Name Data Type Size Format Key Type Index Required
studentID Text 8 Compound Key Yes(duplicates OK) Yes
courseCode Text 8 Compound Key Yes(duplicates OK) Yes
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SQL Create Table
CREATE TABLE tblStudentCourse (studentID VARCHAR(8), courseCode VARCHAR(8),
PRIMARY KEY (studentID, courseCode) );
CREATE TABLE tblStudentCourse (studentID TEXT(8), courseCode TEXT(8), PRIMARY KEY (studentID, courseCode) );
ALTERNATIVE
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Enforcing Foreign Keys
ALTER TABLE tblStudentCourse
ADD CONSTRAINT courseStudentCourseFK FOREIGN KEY (courseCode)
REFERENCES tblcourse (courseCode);
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Adding data using SQL
INSERT INTO targetTable (Field1, Field2, …) VALUES (Value1, Value2, …)
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Adding data using SQL
Method 1
INSERT INTO tblProduct (prodID, prodDesc, cost)
VALUES (‘ssaay1’, ‘Nut’, 34.50)
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Adding data using SQL
Method 2
INSERT INTO tblProduct
VALUES (‘ssaay2’, ‘screw’, 4.50);
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INSERT INTO tblSupplier
(suppName, suppAdd1, suppAdd2, suppPostCode)
VALUES
(‘Johnsons’, ‘34 Meols Parade’, ‘Meols’, ‘CH47 6AY’)
Adding data using SQL
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Summary
Implementation of a Physical Design Use of SQL Create Table Use of SQL Alter Table to enforce foreign
keys. Student individual work Rest of chapter 6
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REMEMBER
Implementation Test (3), W/B
18th February 2008 (20%)
Group Work Implementation Due 7th March 2008
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