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A Guide to SQL, Seventh Edition
Objectives

Understand the concepts and terminology
associated with relational databases

Create and run SQL commands in Oracle,
Microsoft Access, and MySQL

Create tables using SQL
A Guide to SQL, Seventh Edition
Objectives

Identify and use data types to define columns in
SQL tables

Understand and use nulls

Add rows to tables

Describe a table’s layout using SQL
A Guide to SQL, Seventh Edition
Introduction

Databases are found at school libraries, on the
Internet, and other places where you retrieve data
on a computer

Learn concepts and terminology associated with
relational model for database management

Learn how to create a database by describing and
defining tables and columns
A Guide to SQL, Seventh Edition
Introduction

SQL (Structured Query Language) is a widely used
language for retrieving and manipulating data

SQL was developed in the mid-1970’s for IBM
under the name SEQUEL

Renamed SQL in 1980

Most DBMSs use a version of SQL as their data
manipulation language
A Guide to SQL, Seventh Edition
Introduction

You will learn to assign data types to columns and
the use of null values

You will learn how to load a database by creating
tables and adding data to them

You will learn how to describe a table’s layout
using SQL
A Guide to SQL, Seventh Edition
Relational Databases

A relational database is a collection of tables

Tables are called relations

This term is the basis for the name relational
database
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
Entities, Attributes, and Relationships

An entity is a person, place, object, event, or idea
for which you want to store and process data

Premier Product’s entities are customers, orders,
parts, and sales reps

Entities for a school would be students, faculty,
and classes
A Guide to SQL, Seventh Edition
Entities, Attributes, and Relationships

Attribute is a character or property of an entity

Premiere Products attributes for the entity
“customer” are customer name, street, city, and
so on

Also called a field or column in many database
systems
A Guide to SQL, Seventh Edition
Entities, Attributes, and Relationships

A relationship is the association between entities

At Premiere Products, there is a relationship
between customers and sales reps

One-to-many relationship
• Each sales rep has many customers
• Each customer has only one sales rep
A Guide to SQL, Seventh Edition
Entities, Attributes, and Relationships

Premiere Products database

One table for sales reps, one for customers, and
so on for each entity

Attributes become columns in each table

Relationship is represented by using common
columns in two or more tables
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
Definitions

A relation is a two-dimensional table in which:

Entries are single-valued

Each column has a distinct name

All values of the same attribute

Order of columns and rows is immaterial

Each row is distinct
A Guide to SQL, Seventh Edition
Definitions

A relational database is a collection of relations

A row in a table is called a record or a tuple

Multiple entries in one position in a table are called
a repeating group
A Guide to SQL, Seventh Edition
Shorthand Representation

After the name of the table, the columns are listed
within a set of parentheses

REP (Rep_Num, Last_Name, First_Name, Street,
City, State, ZIP, Commission_Rate)

CUSTOMER (Customer_Num, Customer_Name,
Street, City, State, ZIP, Balance, Credit_Limit,
Rep_Num)
A Guide to SQL, Seventh Edition
Shorthand Representation

Not case-sensitive except when inserting character
values in a table

Use a period to separate the table and column
name to avoid confusion

The primary key uniquely identifies a row in a table

Indicate primary key by underlining the column or
collection of columns
A Guide to SQL, Seventh Edition
Database Creation

Describe the layout of each table in the database

Use CREATE TABLE command

TABLE is followed by the table name

Follow this with the names and data types of the
columns in the table

Data types define type and size of data
A Guide to SQL, Seventh Edition
Table and Column Name Restrictions

Names cannot exceed 18 characters

In Oracle, can be up to 30 characters in length

Must start with a letter

Can contain letters, numbers, and underscores (_)

Cannot contain spaces
A Guide to SQL, Seventh Edition
Create Table Command
A Guide to SQL, Seventh Edition
Create Table Command

Table name is REP

Contains nine columns: REP_NUM, LAST_NAME,
FIRST_NAME, STREET, CITY, STATE, ZIP,
COMMISSION, RATE

REP_NUM is limited to two characters and is the
primary key

RATE column is limited to numbers, three digits
with two decimal places
A Guide to SQL, Seventh Edition
Create Table Command

Commands are free-format; no rules stating
specific words in specific positions

Hit enter to move to the next line in a command

Indicate the end of a command by typing a
semicolon
A Guide to SQL, Seventh Edition
Running SQL Commands

Programs and individual preference determine
method for running command

Oracle 10g use SQL*Plus or SQL*Plus Worksheet

Create queries in SQL view in Microsoft Access

Commands are typed at prompt in MySQL
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
Editing SQL Commands

Edit commands as you would in a word processor
when using Oracle SQL*Plus Worksheet or Access
SQL

After making edits, click the Execute or Run button

With Oracle SQL*Plus or MySQL the on-screen
command must be edited to change it
A Guide to SQL, Seventh Edition
Editing Oracle SQL*Plus

In Oracle SQL*Plus you must edit commands one
line at a time

The most recent command is stored in the
command buffer (the buffer)

Edit the command in the buffer by using editing
commands
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
Editing MySQL Commands

Most recent command is stored in memory area
called statement history

Edit command in statement history by using
specific editing commands
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
Editing MySQL Commands

Press Up arrow key to go to top line

Hit Enter key to move to next line if line is correct

Use Right and Left arrow keys to move to point
needing correction

When line is correct hit Enter key

If Enter is not hit on a line, that line will not be part
of the revised command
A Guide to SQL, Seventh Edition
Dropping a Table

Another way to correct errors is to drop (delete) a
table and start over

Useful when table is created before errors are
discovered

Command is followed by the table to be dropped
and a semicolon

Data is deleted when a table is dropped
A Guide to SQL, Seventh Edition
Data Types

For each column, the type of data must be defined

Actual data types vary between SQL programs 
there are some common types

CHAR(n), DATE, DECIMAL(p,q), INTEGER,
SMALLINT
A Guide to SQL, Seventh Edition
Nulls

A null is used as special value to represent
situation when actual value is not known for a
column

Specify whether to allow nulls in the individual
columns

Nulls should not be allowed for primary key
columns
A Guide to SQL, Seventh Edition
Implementation of Nulls

NOT NULL clause is used in a CREATE TABLE
command to exclude the use of nulls in a column

Default is to allow null values

If a column is defined as NOT NULL, system will
reject any attempt to store a null value there
A Guide to SQL, Seventh Edition
Loading a Table with Data

INSERT Command

Adds rows to a table

INSERT INTO followed by the table name

VALUES command follows with specific values in
parentheses

Values for character columns are in single
quotation marks
A Guide to SQL, Seventh Edition
The Insert Command
A Guide to SQL, Seventh Edition
Modifying the INSERT Command

To add new rows it is easier to modify previous
insert command and execute it

Oracle SQL*Plus Worksheet and Access SQL
view, select the text, modify and execute

Oracle SQL*Plus or MySQL, edit commands
manually
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
The INSERT Command with Nulls

Use a special format of INSERT command to enter
a null value in a table

Identify the names of the columns that accept nonnull values, then list only the non-null values after
the VALUES command
A Guide to SQL, Seventh Edition
The INSERT Command with Nulls


Enter only non-null values
Precisely indicate values you are entering by
listing the columns
A Guide to SQL, Seventh Edition
Viewing Table Data

SELECT command is complex

A simple version can display all the rows and
columns in a table

SELECT*FROM followed by the name of the table
with the data you want to view

As with other SQL commands, it ends with a
semicolon
A Guide to SQL, Seventh Edition
Correcting Errors in the Database

UPDATE command is used to update a value in a
table

DELETE command allows you to delete a record

INSERT command allows you to add a record
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
Saving SQL Commands

Allows you to use commands again without
retyping

Different methods for each SQL implementation
you are using

Oracle SQL*Plus and SQL*Plus Worksheet use a
script file

Access saves queries as objects

MySQL uses an editor to save text files
A Guide to SQL, Seventh Edition
Creating the Remaining Tables

Execute appropriate CREATE TABLE and INSERT
commands

Save these commands on your hard drive or a
floppy disk for backup
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
A Guide to SQL, Seventh Edition
Describing a Table

When working with a table, there may not be
access to the CREATE TABLE command used for
the table

Examining the table’s structure will show details
about the columns

Each DBMS has a method to examine a table’s
structure
A Guide to SQL, Seventh Edition
Describing a Table

Oracle SQL*Plus and SQL*Plus Worksheet use
DESCRIBE command

Access uses the Documenter

MySQL uses the SHOW COLUMNS command
A Guide to SQL, Seventh Edition
Summary

Use the CREATE TABLE command to create
tables

DROP TABLE, INSERT, SELECT, UPDATE and
DELETE commands are used to edit tables

Display a table’s structure and layout for
information
A Guide to SQL, Seventh Edition