Learning Database Management Systems In Easy Ways: for Beginners

by Rajeev Kumar

This is a book written for all types of persons related to Business, Education, Management and students of all ages for designing a good database or to develop an application.
In order to develop a good database design application, a well-designed database is very necessary. A properly designed database can be expanded to meet the challenges of any situation, which is possible if and only if you have mastered Database Management Systems - which would be possible if and only if mastering of three areas such as database design, SQL and programming is done.
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Previously, we had been using the system which was file based or traditional one - there were lots of problems for data sharing.
In those days, there were not centralized DBMS ,so problems of sharing data could have been very vital - users had to move from one place to other place - but in case of centralized data users not only using sharing of data but also having reduced or risks arising due to moving from one place to other place .
Undoubtedly, The centralized DBMS will have been very beneficial to users as they were using data shared at one system while applying laws of protection and integrity of the system - who had been using file based system previously and not satisfied with it due to application of different types of protection policies at different systems and data were not sharable at one place rather than would have been be kept at different systems or machines which possible be arising the problems related to redundancy and consistency ,but also very limited to some users. In other words, the scheme failed when there were larger numbers of users working at the same time or problems arised as no policies were then sufficient to provide or enforce rules and regulations for retaining security and integrity of the system while applying recovery procedures and integrity constraints or offering specific perissions to some specific users -then keeping that thing , Distributed Database Approach or system then developed and used today .
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The job of database administrator is to control the entire system while providing privileges to according to users - who can be programmers, operators, end users - and providing integrity constraints.
He provides the rules while providing specific type of permission or right to specific type of user.
He also provide some policies or procedures in the system - if any how some types of failures take place in the system due to human beings or natural disasters or hardware failures - which can recover the same.
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some functions used in SQL are
AVG
SQL>select AVG(t_sal) "average age" from teacher; //average age in teacher table
average age
30
MIN
SQL>select MIN(t_sal) "minimum age" from teacher; //minium age in teacher table
minimum age
25
MAX
SQL>select MAX(t_sal) "maximum age" from teacher; //maximum age in teacher table
maximum age
35
COUNT
SQL>select COUNT(*) "total rows" from teacher; // total rows in teacher table
total rows
2
......
SQL>select * from adn01.student; // Now select statement is written by user user01
S_ID S_NAME S_AGE
soo1 manoj verma 18
soo2 reena arora 19
2 rows selected.
And we get the above data– the administrator adn01 has granted object privileges to user user01.
SQL>disconn // disconnection is made by user user01
Disconnected from oracle //system message to user user01
SQL>Conn // connection is made by adn01
Enter User- Name: adn01 // administrator enter user name
Enter password: *** // administrator enter password
Connected //system mes

18 pages, Kindle Edition

First published December 30, 2014