database systems-lec5

8/14/2019 Database Systems-Lec5

1/60

Chapter 3

Structured Query Language

(SQL)


2/60

2

Introduction to SQL

SQL functions fit into two broad

categories:

1. Data definition language SQL includes commands to create

Database objects such as tables, indexes, and

views

Commands to define access rights to thosedatabase objects

Data manipulation language

Includes commands to insert, update, delete,

and retrieve data within the database tables


3/60

3

Introduction to SQL (continued)

SQL is relatively easy to learn

Basic command set has a vocabulary of

less than 100 words

Nonprocedural language

American National Standards Institute(ANSI) prescribes a standard SQL

Several SQL dialects exist


4/60

4

SQL Data Definition Commands


5/60

5

Data Manipulation Commands


6/60

6

Data Definition Commands

Examine the simple database model

(Figure 6.1) and the database tables that

will form the basis for the many SQL

examples

Understand the data environment


7/60

7

The Database Model


8/60

8

Creating the Database

Two tasks must be completed

create the database structure

create the tables that will hold the end-userdata

First task

RDBMS creates the physical files that willhold the database

Tends to differ substantially from oneRDBMS to another


9/60

9

Creating Database Structures

CREATE DATABASE ;

Example:

CREATE DATABASE SAMPLE1;


10/60

10

Data Types

Data type selection is usually dictated by

the nature of the data and by the intended

use

Pay close attention to the expected use of

attributes for sorting and data retrieval

purposes


11/60

11

Some Common SQL Data Types

DATE

VARCHAR(L)

CHAR(L)

DECIMAL

(L,D)

SMALLINT

INTEGER

Format

Year 0001 9999

Month 01 12

Day 01 - 31

VARCHAR(5)If Ali, database keeps 3 space

only.

CHAR(5)

If Ali, database keeps Ali__ 2

space wasted.

DECIMAL(5,2) 123.45

-32 768 32 767

-2 147 483 648+2 147 483 647

Description

Date

Characte

r

Numeric

Data Type


12/60

12

Some Common SQL Data Types


13/60

13

Creating Table Structures

Use one line per column (attribute) definition

Use spaces to line up the attribute characteristics andconstraints

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 a semicolon


14/60

14

Other SQL Constraints

NOT NULL constraint

Ensures that a column does not accept nulls

UNIQUE constraint

Ensures that all values in a column are unique

DEFAULT constraint

Assigns a value to an attribute when a new row is added to atable

CHECK constraint

Validates data when an attribute value is entered


15/60

15

SQL Indexes

When a primary key is declared, DBMSautomatically creates a unique index

Often need additional indexes

Using the CREATE INDEX command, SQLindexes can be created on the basis of anyselected attribute

Composite index Index based on two or more attributes

Often used to prevent data duplication


16/60

16


CREATE TABLE ();

Example:

CREATE TABLE VENDOR(v_code varchar(5) not null primary key,

v_name varchar(20),v_contact varchar(15),

v_areacode integer,

v_phone varchar(10),

v_state char(2),

v_order Char(1));


17/60

17


Example:

CREATE TABLE PRODUCT(

(p_code varchar(10) not null primary key,

p_descript varchar(50),

p_indate date,

p_onhand integer,

p_min integer,

p_price decimal(5,2),

p_discount decimal (3,2),

v_code varchar(5),

foreign key (v_code) references vendor

on delete restrict);


18/60

18

Data Manipulation Commands

Adding table rows

Saving table changes

Listing table rows Updating table rows

Restoring table contents

Deleting table rows

Inserting table rows with a select

subquery


19/60

19

Common SQL Data

Manipulation Commands


20/60

20

A Data View and Entry Form


21/60

21

Inserting Table Rows

Data Entry

INSERT INTO VALUES (attribute 1 value, attribute 2

value, etc.);

Examples: INSERT INTO VENDOR

VALUES(21225, Bryson, Inc., Smithson, 615, 223-3234, TN,

Y);

INSERT INTO PRODUCTVALUES(11 QER/31, Power painter, 15 psi., 3-nozzle, 07-02-

1999, 8.5, 109.99, 0.00, 25595);


22/60

22

Saving Table Changes

Changes made to table contents are not

physically saved on disk until

Database is closed

Program is closed

COMMIT command is used

Syntax

COMMIT [table names]

Example: COMMIT PRODUCT;

Will permanently save any changes made to

any table in the database.


23/60

23

Listing Table Rows

SELECT

Used to list contents of table

Syntax

SELECT columnlistFROM tablename

Columnlist represents one or more attributes,separated by commas

Asterisk can be used as wildcard character tolist all attributes


24/60

24

Listing Table Rows

Examples:

SELECT * FROM PRODUCT;

SELECT P_CODE, P_DESCRIPT, P_INDATE,P_ONHAND, P_MIN, P-PRICE, P_DISCOUNT,

V_CODE FROM PRODUCT;


25/60

25

Updating Table Rows

UPDATE Modify data in a table

Syntax UPDATE tablename

SET columnname = expression [, columname = expression][WHERE conditionlist];

Examples:

UPDATE PRODUCT SET P_INDATE = 12/11/96WHERE P_CODE = 13-Q2/P2;

If more than one attribute is to be updated inthe row, separate corrections with commas. Examples:

UPDATE PRODUCT SET P_INDATE = 12/11/96, P_PRICE = 15.99,P_MIN=10 WHERE P_CODE = 13-Q2/P2;


26/60

26

Restoring Table Contents

ROLLBACK

Used restore the database to its previous

condition

Only applicable if COMMIT command has notbeen used to permanently store the changes in

the database

Syntax

ROLLBACK;

COMMIT and ROLLBACK only work with data

manipulation commands that are used to add,

modify, or delete table rows


27/60

27

Deleting Table Rows

DELETE

Deletes a table row

Syntax DELETE FROM tablename

[WHERE conditionlist];

Examples:

DELETE FROM PRODUCT WHERE P_CODE = 2238/QPD; DELETE FROM PRODUCT WHERE P_MIN = 5;

WHERE condition is optional

If WHERE condition is not specified, all rows from thespecified table will be deleted.


28/60

28

Inserting Table Rows with a

Select Subquery INSERT

Inserts multiple rows from another table(source)

Uses SELECT subquery Query that is embedded (or nested) inside another

query

Executed first

Syntax INSERT INTO tablename SELECT columnlist

FROM tablename


29/60


30/60

30

Selected PRODUCT Table

Attributes for VENDOR Code21344

SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE

FROM PRODUCT

WHERE V_CODE = 21344;


31/60

31

Comparison Operators



32/60

32


Attributes for VENDOR Codes

Other than 21344

SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE

FROM PRODUCTWHERE V_CODE 21344;



33/60

33


Attributes

with a P_PRICE Restriction

SELECT P_DESCRIPT, P_ONHAND, P_MIN, P_PRICE

FROM PRODUCT

WHERE P_PRICE


34/60

34


Attributes:

The ASCII Code Effect

SELECT P_DESCRIPT, P_ONHAND, P_MIN, P_PRICE

FROM PRODUCTWHERE P_CODE < 1558-QW1;


35/60

35


Attributes: Date Restriction

SELECT P_DESCRIPT, P_ONHAND, P_MIN, P_PRICE, P_INDATE

FROM PRODUCT

WHERE P_INDATE >= 20-Jan-2004;


36/60

36

SELECT Statement

with a Computed Column

SELECT P_DESCRIPT, P_ONHAND, P_PRICE, P_ONHAND* P_PRICE

FROM PRODUCT;


37/60

37

SELECT Statement with a

Computed Column and an Alias

SELECT P_DESCRIPT, P_ONHAND, P_PRICE, P_ONHAND*

P_PRICE AS TOTAL VALUE

FROM PRODUCT;


38/60


39/60

39

Arithmetic Operators:

The Rule of Precedence Perform operations within parentheses

Perform power operations

Perform multiplications and divisions

Perform additions and subtractions



40/60

40


Attributes:

The Logical ORSELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE

FROM PRODUCT

WHERE V_CODE = 21344 OR V_CODE = 24288;


41/60



42/60

42


Attributes:

The Logical AND and ORSELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE

FROM PRODUCT

WHERE (P_PRICE < 50 AND P_DATE > 15-Jan-2004)

OR V_CODE = 24288;


43/60

43

Special Operators BETWEEN

Used to check whether attribute value is withina range

IS NULL Used to check whether attribute value is null

LIKE Used to check whether attribute value

matches a given string pattern

IN

Used to check whether attribute valuematches any value within a value list

EXISTS Used to check if a subquery returns any rows


44/60


45/60

45

Special Operators

IS NULL is used to check whether an attribute

value is null.

Examples:SELECT P_CODE, P_DESCRIPT, V_CODE

FROM PRODUCT

WHERE V_CODE IS NULL;

SELECT P_CODE, P_DESCRIPT, P_INDATE

FROM PRODUCT

WHERE P_INDATE IS NULL;


46/60

46

Special Operators

LIKE is used to check for similar character

strings.

Examples:

SELECT V_NAME, V_CONTACT, V_AREACODE, V_PHONE

FROM VENDOR

WHERE V_CONTACT LIKE Smith%;

SELECT V_NAME, V_CONTACT, V_AREACODE, V_PHONE

FROM VENDOR

WHERE V_CONTACT LIKE SMITH%;


47/60

47

Special Operators

IN is used to check whether an attribute value

matches a value contained within a (sub)set

of listed values.SELECT *

FROM PRODUCT

WHERE V_CODE IN (21344, 24288);

EXISTS is used to check whether an attributehas value.

DELETE FROM PRODUCT WHERE P_CODE EXISTS;

SELECT * FROM PRODUCT WHERE V_CODE EXISTS;

Ad d D t D fi iti


48/60

48

Advanced Data Definition

Commands All changes in the table structure are

made by using the ALTER command

Followed by a keyword that producesspecific change

Three options are available

ADD

MODIFY

DROP

Ch i C l D t


49/60

49

Changing a Columns Data

Type ALTER can be used to change data type

Some RDBMSs (such as Oracle) do not

permit changes to data types unless thecolumn to be changed is empty


50/60

50

Changing a Columns Data

Characteristics

Use ALTER to change data characteristics

ALTER TABLE MODIFY ( );

If the column to be changed already contains data, changes inthe columns characteristics are permitted if those changes donot alter the data type

Examples: Changing a Columns Data Type

ALTERTABLE PRODUCT MODIFY (V_CODE CHAR(5));

Changing Attribute Characteristics

ALTER TABLE PRODUCT MODIFY (P_PRICEDECIMAL(9,2));

Adding a New Column to the Table

ALTER TABLE PRODUCT ADD (P_SALECODE CHAR(1));

Th Eff t f D t E t i t th


51/60

51

The Effect of Data Entry into the

New P_SALECODE Column

UPDATE PRODUCT

SET P_SALECODE = 2

WHERE P_CODE = 1546-QQ2;

U d t f th P SALECODE


52/60

52

Update of the P_SALECODE

Column in Multiple Data Rows

UPDATE PRODUCT SET P_SALECODE = 1

WHERE P_CODE IN (2232/QWE, 2232/QTY);

e ect o u t p e ata


53/60

53

e ect o u t p e ataUpdates in the PRODUCT

Table (MS Access)

UPDATE PRODUCT

SET P_SALECODE = 2WHERE P_INDATE < 25-Dec-2003;

UPDATE PRODUCT

SET P_SALECODE = 1WHERE P_INDATE >= 16-Jan-2004 AND

P_INDATE < 10-Feb-2004;

e ect o u t p e ata


54/60

54

e ect o u t p e ataUpdates in the PRODUCT

Table (MS Access)


55/60

55

Copying Parts of Tables

SQL permits copying contents of selected

table columns so that the data need not

be reentered manually into newly created

table(s)

First create the PART table structure

Next add rows to new PART table using

PRODUCT table rows

PART Attributes Copied


56/60

56


from the PRODUCT Table

CREATE TABLE PART (

PART_CODE CHAR(8) NOT NULL,

PART_DESCRIPT CHAR(35),PART_PRICE DECIMAL(8,2),

PRIMARY KEY(PART_CODE));

INSERT INTO PART (PART_CODE, PART_DESCRIPT, PART_PRICE)

SELECT P_CODE, P_DESCRIPT, P_PRICE

FROM PRODUCT;



57/60

57


from the PRODUCT Table


58/60

58

Adding or Dropping a Column

Use ALTER to add a column

Do not include the NOT NULL clause for new column

Examples:ALTER TABLE PRODUCT ADD PRIMARY KEY (P_CODE);

ALTER TABLE PRODUCT ADD FOREIGN KEY (V_CODE) REFERENCES

VENDOR;

ALTER TABLE PRODUCT ADD PRIMARY KEY (P_CODE) ADD FOREIGN KEY(V_CODE) REFERENCES VENDOR;


59/60

59

Adding or Dropping a Column

Use ALTER to drop a column

Some RDBMSs impose restrictions on the

deletion of an attribute

DROP TABLE ;

Example:

DROP TABLE PART;

R f


60/60

60

References

ROB, P. AND CORONEL, C., 2004, Database

Systems. 6th Ed., Thomson Course Technology

database systems-lec5

Documents