Database Assignment-2.doc

8/9/2019 Database Assignment-2.doc

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Q1) Write 15 select Syntax and define Select Statement.

Ans)The SELECT statement is used to select data from a database.

The result is stored in a result table, called the resultset.

SELECT ! "#$% table&name

1) Select 'Column&name( from 'table&name(

*) Select 'Column&name( from 'table&name( +here 'condition(

) Select 'Column&name( from 'table&name( +here 'condition(

li-e 'attern(

/) Select 'Column&name( from 'table&name( +here 'condition(order by 'exression(

5) Select 'Column&name( from 'table&name( +here 'condition(

0rou by 'exression(

) Select 'Column&name( from 'table&name( +here 'condition(

ha2in0 'exression(

3) Select 'Column&name1( from 'table&name1( %inus

Select 'Column&name*( from 'table&name*(

4) Select 'Column&name1( from 'table&name1( ntersectSelect 'Column&name*( from 'table&name*(

6) Select 'Column&name1( from 'table&name1( 7nion


18) Select 'Column&name1( from 'table&name1( 7nion All


9*) Write different S9L Statements +ith Examle and define it.

Ans) What is SQL? SQL stands for Structured Query Language SQL lets you access and manipulate databases SQL is an ANSI (American National Standards Institute) standard

SQL Statements

1) Select Statement

2) :elete Statement;DELETE F!" table#name $%EE some#column&some#'alue

3) Commit4) #ollbac-


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5) Alter; ALTE TALE table#name ENA"E T! ne#table#name

6) 7date; *+DATE table#name SET column,&'alue- column.&'alue.-/// $%EE some#column&some#'alue

7) %odify; Alter TABLE "table_name" ALTER COLUMN "colmn !" "Ne #ata T$%e

8) 7nion;SELECT #ate &ROM Store_'n(ormation UN'ON

SELECT #ate &ROM 'nternet_Sales

9) 7nion All;SELECT #ate &ROM Store_'n(ormation UN'ON ALL SELECT #ate &ROM 'nternet_Sales

10) ntersect;SELECT #ate &ROM Store_'n(ormation 'ntersect

SELECT #ate &ROM 'nternet_Sales11) %inus;SELECT #ate &ROM Store_'n(ormation

MinsSELECT #ate &ROM 'nternet_Sales

12) Where

13) Li-e

Q3) :efine Tri00er, tyes of Tri00er .syntax of tri00ers +ith examles

Tri00ers

Ans)Tri00ers are named database ob:ATE statement iserformed on the table. %yS9L does not ermit t+o tri00ers +ith the


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same tri00er timin0 ?@E"$#E or A"TE#) and tri00er e2ent or

statement ?=SE#T, :ELETE, or 7>:ATE) to be defined on a table.

"or examle, you cannot define t+o @E"$#E =SE#T or t+o

A"TE# 7>:ATE tri00ers for a table. All tri00ers defined on %yS9L

are ro+ tri00ers, +hich mean that the action defined for the tri00ers is

executed for each ro+ affected by the tri00erin0 statement.

Error handlin0 durin0 tri00er execution for transactional tables

ensures that either both the tri00erin0 statement and tri00er action is

comleted successfully or neither the tri00er statement nor the tri00er

action is executed, that is all chan0es made are rollbac- on failure. "or

nontransactional tables, all chan0es made rior to the oint of error

remains in effect.

Tyes of Tri00ers in $racle

1. @efore Tri00er

*. After Tri00er

. #o+ le2el tri00er

/. Schema Tri00er

5. nstead of Tri00er

. :atabase Tri00er

3. Statement le2el Tri00er

The follo+in0 is the syntax to create a tri00er

C#EATE T#E# 'tri00er name(

B @E"$#E A"TE# D

B =SE#T 7>:ATE :ELETE D

$= 'table name(

"$# EAC #$W

'tri00ered action(


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n $racle, tri00ers can be fired +hen one of the follo+in0 oerations

occurs;

:%L statements ?=SE#T, :ELETE or 7>:ATE) that modify

data on a table or 2ie+ ::L statements

7ser e2ents such as lo0on and lo0off

System e2ents such as startu, shutdo+n, and error messa0es

$racle allo+s multile tri00ers +ith the same tri00er timin0 and

tri00er e2ent to be defined on a table ho+e2er, these tri00ers are not

0uaranteed to execute in any secific order. Tri00ers can be defined as

ro+ tri00ers or statement tri00ers. Statement tri00ers are fired once

for each tri00erin0 statement re0ardless of the number of ro+s in a

table affected by the tri00erin0 statement. "or examle if a :ELETE

statement deletes se2eral ro+s from a table, a statement tri00er is only

fired once.

The execution model for $racle tri00ers is transactional. All actions

erformed as a result of the tri00erin0 statement, includin0 the actionserformed by fired tri00ers, must all succeed other+ise, they are

rolled bac-.

Q4) :efine rocedure, syntax of rocedure and difference bet+een

rocedure and stored rocedure.

Ans)A rocedure is a subro0ram that erforms a secific action.

Fou must declare and define a rocedure before in2o-in0 it. Fou can

either declare or define it at the same time, or you can declare it first

and then define it later in the same bloc- or subro0ram.

Syntax

>rocedure declaration; G


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>rocedure headin0; G

>rocedure definition; G

Hey+ord and >arameter :escritions

@ody

The reIuired executable art of the rocedure and, otionally, the

excetionhandlin0 art of the rocedure.

:eclare section

The otional declarati2e art of the rocedure. :eclarations are local

to the rocedure, can be referenced in body, and cease to exist +hen

the rocedure comletes execution.

>rocedure declaration

:eclares a rocedure, but does not define it. The definition must

aear later in the same bloc- or subro0ram as the declaration.

A rocedure declaration is also called a rocedure secification, or

rocedure sec.

>rocedure definition

Either defines a rocedure that +as declared earlier in the same bloc-

or subro0ram, or declares and defines a rocedure.

>rocedure name


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The name that you 0i2e to the rocedure that you are declarin0 or

definin0.

Stored Procedures

Stored rocedures ro2ide a o+erful +ay to code alication lo0ic

that can be stored on the ser2er. %yS9L and $racle both use stored

rocedures and functions. Stored functions are similar to rocedures,

excet that a function returns a 2alue to the en2ironment in +hich it is

called. n %yS9L, stored rocedures and functions are collecti2ely

called routines.

The follo+in0 sections comare stored rocedures in %yS9L and$racle;

ndi2idual S9L Statement

Jariables in stored >rocedures

Error andlin0 in Stored >rocedures

3.2.1 Individual SQ State!ents

This section describes considerations related to the follo+in0

statements or constructs;

#E>LACE Statement

:$ Statement

Comound :ECLA#E Statement

Comound SET Statement

3.2.1.1 REPLACE Statement

The #E>LACE statement in %yS9L is a dualurose statement. t

+or-s li-e the =SE#T statement +hen there is no record in the table

that has the same 2alue as the ne+ record for a rimary -ey or a

uniIue index, and other+ise it +or-s li-e the 7>:ATE statement.


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$racle does not ha2e any builtin S9L statements that suorts the

uroses of the %yS9L #E>LACE statement. To con2ert this

statement to $racle, an emulated function usin0 both the =SE#T and

7>:ATE statements has to be created. An attemt is first made to

lace the data into the table usin0 the =SE#T statement and if this

fails, the data in the table is then udated usin0 the 7>:ATE

statement.

DO Statement

As its name imlies, the :$ statement in %yS9L does somethin0 but

does not return anythin0 secifically, it executes the comma

delimited list of exressions secified as its arameters. The :$statement is con2erted to a SELECT exr1 K, exr*,M =T$

"#$% :7AL statement in $racle.

Compound DECLARE Statement

%yS9L uses the :ECLA#E statement to declare local 2ariables in

stored rocedures. >LNS9L does not allo+ multile declarations each

declaration must be made searately. To con2ert comound

:ECLA#E statements into functionally eIui2alent >LNS9L code,each %yS9L multile declaration statement should be con2erted into

lo0ically eIui2alent searate statements, one for each declaration.

"or examle, consider the follo+in0 %yS9L simle declaration and

multile declaration statements;

N! Simle declaration !N

:ECLA#E a =T

N! Comound declaration !N

:ECLA#E a, b =T :E"A7LT 5

The >LNS9L functionally eIui2alent statements are;

N! Simle declaration !N

a =T


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N! %ultile declarations !N

a =T ;G 5

b =T ;G 5

Q5):efine the follo+in0 term

1) Concurrency Control

"e#inition

Concurrency control is a database mana0ement systems ?:@%S)

concet that is used to address conflicts +ith the simultaneous

accessin0 or alterin0 of data that can occur +ith a multiuser system.

Concurrency control, +hen alied to a :@%S, is meant to

coordinate simultaneous transactions +hile reser2in0 data inte0rity.

K1M The Concurrency is about to control the multiuser access of:atabase

Illustrative $%a!&le

To illustrate the concet of concurrency control, consider t+o

tra2ellers +ho 0o to electronic rail+ay reser2ation counter at the same

time to urchase a train tic-et to the same destination on the same

train. ThereOs only one seat left in the coach, but +ithout concurrency

control, itOs ossible that both tra2elers +ill end u urchasin0 a tic-etfor that one seat. o+e2er, +ith concurrency control, the database

+ouldnOt allo+ this to haen. @oth tra2ellers +ould still be able to

access the train seatin0 database, but concurrency control +ould

reser2e data accuracy and allo+ only one tra2eler to urchase the

seat.

This examle also illustrates the imortance of addressin0 this issue

in a multiuser database. $b2iously, one could Iuic-ly run into


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roblems +ith the inaccurate data that can result from se2eral

transactions occurrin0 simultaneously and +ritin0 o2er each other.

The follo+in0 section ro2ides strate0ies for imlementin0

concurrency control.

i) Transaction processing

A tye of comuter rocessin0 in +hich the comuter resonds

immediately to user reIuests. Each reIuest is considered to be a

transaction.Automatic teller machines for ban-s are an examle of

transaction rocessin0.

The oosite of transaction rocessin0 is batch rocessin0, in +hich abatch of reIuests is stored and then executed all at one time.

Transaction rocessin0 reIuires interaction +ith a user, +hereas batch

rocessin0 can ta-e lace +ithout a user bein0 resent.

ii) Optimization

The maximiPin0 or minimiPin0 of a 0i2en function ossibly sub


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+ill best satisfy a selected criterion. Also -no+n as system

otimiPation.

An act, rocess, or methodolo0y of ma-in0 somethin0 ?as a desi0n,

system, or decision) as fully erfect, functional, or effecti2e as

ossible secifically; the mathematical rocedures ?as findin0 the

maximum of a function) in2ol2ed in this

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Database Assignment-2.doc