Chapter # 7Introduction to

Structured Query Language (SQL)

Part I

SQL functions fit into two broad categories:

Data definition language

Data manipulation language

Basic command set has vocabulary of less than 100 words

American National Standards Institute (ANSI) prescribes a

standard SQL

Several SQL dialects exist

Introduction to SQL

SQL Family

SQL(Structured Query Language)

Data Definition

Language (DDL)

CREATE

ALTER

DROP

Data Manipulation

Language (DML)

SELECT

INSERT

UPDATE

DELETE

Data Control

Language (DCL)

GRANT

REVOKE

The database model

In this chapter, a simple database with these tables is

used to illustrate commands:

CUSTOMER

INVOICE

LINE

PRODUCT

VENDOR

Focus on PRODUCT and VENDOR tables

Data Definition Commands

Data Definition Commands (2)

Two tasks must be completed:

Create database structure

Create tables that will hold end-user data

First task:

RDBMS creates physical files that will hold database

Differs substantially from one RDBMS to another

Creating the Database

CREATE DATABASE <DATABASENAME>;

CREATE TABLE states (

id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,

state CHAR(25),

population INT(9)

);

Authentication

DBMS verifies that only registered users are

able to access database

Log on to RDBMS using user ID and password created

by database administratorCREATE USER 'jeffrey'@'localhost' IDENTIFIED BY 'password';

GRANT ALL ON db1.* TO 'jeffrey'@'localhost';

Schema

Group of database objects that are related to each other

The Database Schema

Data type selection is usually dictated by

nature of data and by intended use

Supported data types:

Number(L,D), Integer, Smallint, Decimal(L,D)

Char(L), Varchar(L), Varchar2(L)

Date, Time, Timestamp

Real, Double, Float

Interval day to hour

Many other types

Data Types

Use one line per column (attribute) definition

Use spaces to line up attribute characteristics and

constraints

Table and attribute names are capitalized

NOT NULL specification

UNIQUE specification

Primary key attributes contain both a NOT NULL and a

UNIQUE specification

RDBMS will automatically enforce referential integrity for

foreign keys

Command sequence ends with semicolon

Creating Table Structures

Creating Table Structures (Example)

NOT NULL constraint

Ensures that column does not accept nulls

UNIQUE constraint

Ensures that all values in column are unique

DEFAULT constraint

Assigns value to attribute when a new row is added to

table. The end user may, of course, enter a value other

than the default value.

CHECK constraint

Validates data when attribute value is entered

SQL Constraints

In this chapter, Oracle is used to illustrate SQL constraints.

For example, note that the following SQL command

sequence uses the DEFAULT and CHECK constraints to

define the table named CUSTOMER.

SQL Constraints

When primary key is declared, DBMS automatically

creates unique index

Often need additional indexes

Using CREATE INDEX command, SQL indexes can be

created on basis of any selected attribute

Using the CREATE INDEX command, SQL indexes can be

created on the basis of any selected attribute. The syntax

is:

SQL Indexes

CREATE [UNIQUE] INDEX indexname ON tablename(column1 [, column2])

For example, based on the attribute P_INDATE stored in

the PRODUCT table, the following command creates an

index named P_INDATEX: CREATE INDEX P_INDATEX ON PRODUCT(P_INDATE);

Using the UNIQUE index qualifier, you can even create an

index that prevents you from using a value that has been

used before. Such a feature is especially useful when the

index attribute is a candidate key whose values must not

be duplicated: CREATE UNIQUE INDEX P_CODEX ON PRODUCT(P_CODE);

SQL Indexes

INSERT

SELECT

UPDATE

DELETE

ROLLBACK

COMMIT

Data Manipulation Commands

INSERT

Used to enter data into table

Basic Syntax:

Example

Adding Table Rows

INSERT INTO columnname VALUES (value1,

value2, … , valueN);

INSERT INTO VENDORVALUES (21225,'Bryson,

Inc.','Smithson','615','223-3234','TN','Y');

When entering values, notice that:

Row contents are entered between parentheses

Character and date values are entered between

apostrophes

Numerical entries are not enclosed in apostrophes

Attribute entries are separated by commas

A value is required for each column

Use NULL for unknown values

Adding Table Rows (2)

INSERT INTO PRODUCTVALUES ('BRT-345','Titanium drill

bit','18-Oct-09', 75, 10, 4.50, 0.06, NULL);

Changes made to table contents are not physically saved

on disk until:

Database is closed

Program is closed

COMMIT command is used

Syntax:

Saving Table Changes

COMMIT [WORK];

Will permanently save any changes made to any table in

the database

NOTE TO MS ACCESS USERS

MS Access doesn't support the COMMIT

command because it automatically saves

changes after the execution of each SQL

command.

SELECT

Used to list contents of table

Basic Syntax:

Listing (Showing) Table Rows

SELECT columnlist FROM tablename;

Columnlist represents one or more attributes, separated by

commas

Asterisk can be used as wildcard character to list all

attributes

Example:

SELECT * FROM PRODUCT;

THE END