MCS-023 Solved Assignment 2013-14

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Course Code : MCS-023Course Title : Introduction to Database Management SystemsAssignment Number : MCA (2)/023/Assign /13Maximum Marks : 100Weightage : 25%Last Dates for Submission : 15th October, 2013 (For July 2013 Session)

15th April, 2014 (For January 2014 Session)

Question 1: (20 Marks)Design an ER diagram for an XYZ Information Technology Training Institute that will meet the informationneeds for their training programmes. Clearly indicate the entities, relationships, cardinality and the keyconstraints. The description of the environment is as follows:



Question 2:(20 Marks)Staff No.

Branch No. BranchAddress

Name Position Hrs/Week

E101 B02 Sun Plaza,Delhi,110001

Rahul Assistant 16

E101 B04 2/3 UT,Delhi,110111

Rahul Assistant 9

E122 B02 Sun Plaza,Delhi,110001

Medha Assistant 14

E122 B04 2/3 UT,Delhi,110111

Medha Assistant 10

Question 3: (10 Marks)Explain how the “GROUP By” clause works. What is the difference between the WHERE and HAVING clauses?Explain them with the help of an example for each.

Description

The usage of SQL GROUP BY clause is, to divide the rows in a table into smaller groups.

The GROUP BY clause is used with the SQL SELECT statement.

The grouping can happen after retrieves the rows from a table.

When some rows are retrieved from a grouped result against some condition, that is possible with HAVINGclause.

The GROUP BY clause is used with the SELECT statement to make a group of rows based on the values of aspecific column or expression. The SQL AGGREGATE function can be used to get summary information forevery group and these are applied to individual group.

The WHERE clause is used to retrieve rows based on a certain condition, but it can not be applied to groupedresult.

In an SQL statement, suppose you are using GROUP BY, if required you can use HAVING instead of WHERE,after GROUP BY.



Syntax

SELECT <column_list>

FROM < table name >

WHERE <condition>GROUP BY <columns>

[HAVING] <condition>;

Parameters

Name Description

table_name Name of the table.

column_list Name of the columns of the table.

columns Name of the columns which will participate in grouping..



Pictorial Presentation of Groups of Data

Using GROUP BY with Aggregate Functions

- The power of aggregate functions is greater when combined with the GROUP BY clause.- The GROUP BY clause is rarely used without an aggregate function.

SQL GROUP BY with COUNT() function

The following query displays number of employees work in each department.

- See more at: http://www.w3resource.com/sql/group-by.php#sthash.P2dM04IR.dpuf



Where’ and ‘Having’ clause both are used to filter the rows fetched from select statement however there is a difference:

WHERE CLAUSE

Using where clause we can restrict or filter the records that we get from select statement.Let say from the select statement we are fetching 10 records but we wanted to display 3 records.In the below example we are trying to fetch only the employee records for deptno = 10.

Ex:SQL> SELECT *

FROM empWHERE deptno = 10;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO------ ----- ------ ------ ---------- ----- ----- ------

7782 CLARK MANAGER 7839 6/9/1981 2450 10

7839 KING PRESIDENT 11/17/1981 5000 10

7934 MILLER CLERK 7782 1/23/1982 1300 10

HAVING

Before we discuss ‘Having’ clause lets understand ‘Group by’ clause first.Using group by, we can create groups of related information.Columns used in ‘select’ must be used with ‘group by’, otherwise system does not recognize it as a group by expression.In the below example we are trying to display sum of salaries at each dept level.When SQL statement is run, data fetched from the database is grouped first based on deptno and then sum() function is applied to get the desiredresult.Ex:

SQL> SELECT deptno, SUM(sal)FROM empGROUP BY deptno;

DEPTNO SUM(SAL)---------- ----------

10 875020 1087530 9400

In this example we are trying to group the records using two columns deptno and job

SQL> SELECT deptno,job,SUM(sal)FROM empGROUP BY deptno,job;

DEPTNO JOB SUM(SAL)-------- --------- ----------

10 CLERK 1300

10 MANAGER 2450

10 PRESIDENT 5000

20 ANALYST 6000

20 CLERK 1900

20 MANAGER 2975



30 CLERK 950

30 MANAGER 2850

30 SALESMAN 5600

Having Clause:

Having clause is used to restrict the records that are grouped using group by clause.Having clause is just like where clause but it can be used only with group by as we cannot use where clause in group by.Having clause works or can be used, only in the combination with group by clause.

In the below example we are trying to fetch all deptno and job records whose aggregated salary of its employees is greater than 3000 ( Sum(sal)> 3000 ).Having clause gets executed after the records are fetched and grouped.Ex:

SQL> SELECT deptno,job,SUM(sal) tsalFROM empGROUP BY deptno,jobHAVING SUM(sal) > 3000;

DEPTNO JOB TSAL---------- --------- --------

10 PRESIDENT 5000

20 ANALYST 6000

30 SALESMAN 5600

In this example, after applying the having clause we are trying to order the records by JOB.

SQL> SELECT deptno,job,SUM(sal) tsalFROM empGROUP BY deptno,jobHAVING SUM(sal) > 3000

ORDER BY job;

DEPTNO JOB TSAL---------- --------- -------

20 ANALYST 6000

10 PRESIDENT 5000

30 SALESMAN 5600

ORDER OF EXECUTION• Group the rows together based on group by clause.• Calculate the group functions for each group.• Choose and eliminate the groups based on the having clause.• Order the groups based on the specified column.



Question 5: (10 Marks)What are the advantages of indexed-sequential file organisation? With the help of an example explain thestructure of indexed-sequential file.

NDEXED SEQUENTIAL FILE ORGANIZATION

When there is need to access records sequentially by some key value and also to access recordsdirectly by the same key value, the collection of records may be organized in an effective mannedcalled Indexes Sequential Organization.

You must be familiar with search process for a word in a language dictionary. The data in thedictionary is stored in sequential manner. However an index is provided in terms of thumb tabs. Tosearch for a word we do not search sequentially. We access the index that is the appropriatethumb tab, locate an approximate location for the word and then proceed to find the wordsequentially.

To implement the concept of indexed sequential file organizations, we consider an approach inwhich the index part and data part reside on a separate file. The index file has a tree structure anddata file has a sequential structure. Since the data file is sequenced, it is not necessary for theindex to have an entry for each record Following figure shows a sequential file with a two-levelindex.

Level 1 of the index holds an entry for each three-record section of the main file. The level 2indexes level 1 in the same way.

When the new records are inserted in the data file, the sequence of records need to be preservedand also the index is accordingly updated.

Two approaches used to implement indexes are static indexes and dynamic indexes.

As the main data file changes due to insertions and deletions, the static index contents maychange but the structure does not change . In case of dynamic indexing approach, insertions anddeletions in the main data file may lead to changes in the index structure. Recall the change inheight of B-Tree as records are inserted and deleted.

Both dynamic and static indexing techniques are useful depending on the type of application.



Question 6: (10 Marks)Illustrate theIllustrate the differences between Hierarchical, Network and Relational data models with the help of suitableexamples. Explain why relational data model is a better choice over the two. Justify your answer.

the difference between hierarchical data model or network data mode and relational datamodel:

1.The hierarchical data model :The hierarchical data model organizes data in a tree structure. Thereis a hierarchy of parent and child data segments. This structure implies that a record can haverepeating information, generally in the child data segments. Data in a series of records, which have aset of field values attached to it. It collects all the instances of a specific record together as a recordtype. These record types are the equivalent of tables in the relational model, and with the individualrecords being the equivalent of rows. To create links between these record types, the hierarchicalmodel uses Parent Child Relationships. These are a 1:N mapping between record types. This is done byusing trees, like set theory used in the relational model, "borrowed" from maths.

2:the network data model :The popularity of the network data model coincided with the popularityof the hierarchical data model. Some data were more naturally modeled with more than one parent perchild. So, the network model permitted the modeling of many-to-many relationships in data.

3:the relational model:A database based on the relational model developed by E.F. Codd. Arelational database allows the definition of data structures, storage and retrieval operations andintegrity constraints. In such a database the data and relations between them are organized in tables.A table is a collection of records and each record in a table contains the same fields.properties of relational database: 1. Values Are Atomic 2. Each Row is Unique3. Column Values Are of the Same Kind4.The Sequence of Columns is Insignificant 5. The Sequence of Rows is Insignificant6. Each Column Has a Unique Name

Characteristic Hierarchical model Network model Relational model

Data structureWhen we go through the structure of

the hierarchical model we can identify that it used a method for storing data in adatabase that looks like a family tree with one root and a number of branches orsubdivisions. That's why we can say that record types are organized in the formof a rooted tree. But in network model we can identify multiple branches



emanating from one or more nodes. So some times it is like a like several treeswhich share branches. In relational model is that of a relation. Relation is a two-dimensional table. So the table can be used to represent some entity informationor some relationship between them

Data structureOne to many or one to onerelationships

Allowed the network model tosupport many to many relationships

One to One,One to many, Many to manyrelationships

In hierarchical model only one-to-many or one-to-one relationships can be exist. But in network data model makes it possible tomap many to many relationships In relational each record can have multiple parents and multiple child records. In effect, itsupports many to many relationships

Data structure Based on parent child relationshipA record can have many parents aswell as many children.

Based on relational datastructures

In hierarchical model relationship based in terms of parent child. So a child may only have one parent but a parent can havemultiple children. But in network data model a record can have many parents as well as many children. Relational data model isbased on relational data structures

Datamanipulation

Does not provide an independentstand alone query interface

CODASYL (Conference on DataSystems Languages)

Relational databases are whatbrings many sources into acommon query (such as SQL)

In relational database it use powerful operations such as SQL languages or query by example are used to manipulate data stored inthe database But in hierarchical data model it does notprovide an independent stand alone query interface while network model uses CODASYLDatamanipulation

retrieve algorithms are complex andasymmetric

Retrieve algorithms are complex andsymmetric

Retrieve algorithms are simpleand symmetric

In hierarchical data model and network model retrieve algorithms are complex and symmetric But in relational data model retrievealgorithms are simple and symmetric

Data integrityCannot insert the information of achild who does not have any parent.

Does not suffer form any insertionanomaly.

Does not suffer from any insertanomaly.

In hierarchical data model we cannot insert the information of a child who does not have any parent. But in network model doesnot suffer form any insertion anomaly. relational model does not suffer from any insert anomaly

Data integrity

Multiple occurrences of child recordswhich lead to problems ofinconsistency during the updateoperation

Free from update anomalies. Free form update anomalies

In network model it is free from update anomalies because there is only a single occurrence for each record set.In relational modelit also free form update anomalies because it removes the redundancy of data by proper designing through normalization process.But in hierarchical model there are multiple occurrences of child records. which lead to problems of inconsistency during theupdate operation



Data intergirtyDeletion of parent results in deletionof child records

Free from delete anomalies Free from delete anomalies

In hierarchical model it is based on parent child relationship and deletion of parent results in deletion of child records .But innetwork model and in relational model it is free from deletion anomalies. Because information is stored in different tables.

MCS-023 Solved Assignment 2013-14

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