Primary index, Database Management System

Primary index

A primary index is a file that has a sorted series of records having two columns: a block address for that key field in the data file; and the ordering key field. The ordering key field for this primary index can be the primary key of the data file. Primary index have one index entry for every value of the ordering key field. An entry in primary index file has the index value of the pointer to that data block and a first record of the data block.

Let us talk about primary index with the help of an instance. Let us suppose a student database as (Supposing that one block keeps only four student records.):

Enrolment                                                                             Progra- Number                 Name                           City                   mme

BLOCK 1

2109348

ANU VERMA

CHENNAI

CIC

2109349

ABHISHEK KUMAR

CALCUTTA

MCA

2109351

VIMAL KISHOR

KOCHI

BCA

2109352

RANJEETA JULIE

KOCHI

CIC

BLOCK 2

2109353

MISS RAJIYA BANU

VARANASI

MBA

2238389

JITENDAR KASWAN

NEW DELHI

MBA

2238390

RITURAJ BHATI

VARANASI

MCA

2238411

AMIT KUMAR JAIN

NEW DELHI

BCA

BLOCK 3

2238412

PAWAN TIWARI

AJMER

MCA

2238414

SUPRIYA  SWAMI

NEW DELHI

MCA

2238422

KAMLESH KUMAR

MUMBAI

BSC

2258014

DAVEN SINGHAL

MUMBAI

BCA

BLOCK 4

2258015

S SRIVASTAVA

MUMBAI

BCA

2258017

SHWETA SINGH

NEW DELHI

BSC

2258018

ASHISH TIWARI

MUMBAI

MCA

2258019

SEEMA RANI

LUCKNOW

MBA

...

...

...

...

...

BLOCK r

2258616

NIDHI

AJMER

BCA

2258617

JAGMEET SINGH

LUCKNOW

MCA

2258618

PRADEEP KUMAR

NEW DELHI

BSC

2318935

RAMADHAR

FARIDABAD

MBA

...

...

...

...

...

BLOCK N-1

2401407

BRIJMISHRA

BAREILLY

CIC

2401408

AMIT KUMAR

BAREILLY

BSC

2401409

MD. IMRAN SAIFI

AURANGABAD

BCA

2401623

ARUN KUMAR

NEW DELHI

MCA

BLOCK N

2401666

ABHISHEK RAJPUT

MUMBAI

MCA

2409216

TANNUJ SETHI

LUCKNOW

MBA

2409217

SANTOSH KUMAR

ALMORA

BCA

2409422

SAKSHI GINOTRA

MUMBAI

BSC

                                    Figure: A Student file stored in the order of student enrolment numbers

Posted Date: 3/7/2013 6:24:53 AM | Location : United States







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