DBMS Interview Questions and Answers

Database provides a systematic and organized way of storing, managing and retrieving from

collection of logically related information.

Secondly the information has to be persistent, that means even after the application is closed

the information should be persisted.

Finally it should provide an independent way of accessing data and should not be dependent on the application to access the information.

Main difference between a simple file and database that database has independent way (SQL) of accessing information while simple files do not File meets the storing, managing and retrieving part of a database but not the independent way of accessing data. Many experienced programmers think that the main difference is that file can not provide multi-user capabilities which a DBMS provides. But if we look at some old COBOL and C programs where file where the only means of storing data, we can see functionalities like locking, multi-user etc provided very efficiently. So it’s a matter of debate if some interviewers think this as a main difference between files and database accept it… going in to debate is probably loosing a job.

SQL stands for Structured Query Language.SQL is an ANSI (American National Standards

Institute) standard computer language for accessing and manipulating database systems. SQL

statements are used to retrieve and update data in a database.

DBMS provides a systematic and organized way of storing, managing and retrieving from

collection of logically related information. RDBMS also provides what DBMS provides but above that it provides relationship integrity. So in short we can say

RDBMS = DBMS + REFERENTIAL INTEGRITY 

These relations are defined by using “Foreign Keys” in any RDBMS.Many DBMS companies claimed there DBMS product was a RDBMS compliant, but according to industry rules and regulations if the DBMS fulfills the twelve CODD rules it’s truly a RDBMS. Almost all DBMS (SQL SERVER, ORACLE etc) fulfills all the twelve CODD rules and are considered as truly RDBMS.

In 1969 Dr. E. F. Codd laid down some 12 rules which a DBMS should adhere in order to get the logo of a true RDBMS.

"All information in a relational data base is represented explicitly at the logical level and in

exactly one way - by values in tables."

"Each and every datum (atomic value) in a relational data base is guaranteed to be logically

accessible by resorting to a combination of table name, primary key value and column name."

In flat files we have to parse and know exact location of field values. But if a DBMS is truly

RDBMS you can access the value by specifying the table name, field name, for instance

Customers.Fields [‘Customer Name’].

"Null values (distinct from the empty character string or a string of blank characters and distinct from zero or any other number) are supported in fully relational DBMS for representing missing information and inapplicable information in a systematic way, independent of data type.". 

"The data base description is represented at the logical level in the same way as ordinary data, so that authorized users can apply the same relational language to its interrogation as they apply to the regular data."The Data Dictionary is held within the RDBMS, thus there is no-need for off-line volumes to tell you the structure of the database.

"A relational system may support several languages and various modes of terminal use (for

example, the fill-in-the-blanks mode). However, there must be at least one language whose

statements are expressible, per some well-defined syntax, as character strings and that is

comprehensive in supporting all the following items.