Database Interview Questions And Answers

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Top Database interview questions and answers for freshers and experienced

What is Database ?

Answer : database is an organized collection of data typically used to model certain situations. Use this tag if you have questions about designing a database. If it is about a particular database management system, (e.g., MySQL), please use that tag instead

Questions : 1 :: What is database?

A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific...View answers

Questions : 2 :: What is a Database system?

The database and DBMS software together is called as Database system.

Questions : 3 :: What are the advantages of DBMS?


Redundancy is controlled. Unauthorised access is restricted. Providing multiple user interfaces. Enforcing integrity constraints. Providing backup and...View answers

Questions : 4 :: What are the disadvantage in File Processing System?

Data redundancy and inconsistency. Difficult in accessing data. Data isolation. Data integrity. Concurrent access is not possible. Security...View answers

Questions : 5 :: Describe the three levels of data abstraction?

The are three levels of abstraction: Physical level: The lowest level of abstraction describes how data are stored. Logical level: The next higher level of abstraction, describes what data are...View answers

Questions : 6 :: Define the "integrity rules"?


There are two Integrity rules. Entity Integrity: States that "Primary key cannot have NULL value" Referential Integrity: States that "Foreign Key can be either a NULL value or should be...View answers

Questions : 7 :: What is extension and intension?

Extension: It is the number of tuples present in a table at any instance. This is time dependent. Intension: It is a constant value that gives the name, structure of table and the constraints laid...View answers

Questions : 8 :: What is System R? What are its two major subsystems?

System R was designed and developed over a period of 1974-79 at IBM San Jose Research Center. It is a prototype and its purpose was to demonstrate that it is possible to build a Relational System...View answers

Questions : 9 :: How is the data structure of System R different from the relational structure?


Unlike Relational systems in System R Domains are not supported Enforcement of candidate key uniqueness is optional Enforcement of entity integrity is optional Referential integrity is not...View answers

Questions : 10 :: What is Data Independence?

Data independence means that "the application is independent of the storage structure and access strategy of data". In other words, The ability to modify the schema definition in one level should...View answers

Questions : 11 :: What is a view? How it is related to data independence?

A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no...View answers

Questions : 12 :: What is Data Model?

A collection of conceptual tools for describing data, data relationships data semantics and constraints.

Questions : 13 :: What is E-R model?

This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.

Questions : 14 :: What is Object Oriented model?

This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These...View answers

Questions : 15 :: What is an Entity?

It is a 'thing' in the real world with an independent existence.

Questions : 16 :: What is Data Storage - Definition Language?

The storage structures and access methods used by database system are specified by a set of definition in a special type of DDL called data storage-definition language.

Questions : 17 :: What is DML (Data Manipulation Language)?

This language that enable user to access or manipulate data as organised by appropriate data model. Procedural DML or Low level: DML requires a user to specify what data are needed and how to get...View answers

Questions : 18 :: What is DML Compiler?

It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.

Questions : 19 :: What is DDL Interpreter?

It interprets DDL statements and record them in tables containing metadata.

Questions : 20 :: What is Record-at-a-time?

The Low level or Procedural DML can specify and retrieve each record from a set of records. This retrieve of a record is said to be Record-at-a-time.

Questions : 21 :: What is Set-at-a-time or Set-oriented?

The High level or Non-procedural DML can specify and retrieve many records in a single DML statement. This retrieve of a record is said to be Set-at-a-time or Set-oriented.

Questions : 22 :: What is Relational Algebra?

It is procedural query language. It consists of a set of operations that take one or two relations as input and produce a new relation.

Questions : 23 :: What is Relational Calculus?

It is an applied predicate calculus specifically tailored for relational databases proposed by E.F. Codd. E.g. of languages based on it are DSL ALPHA, QUEL.

Questions : 24 :: How does Tuple-oriented relational calculus differ from domain-oriented relational calculus?

The tuple-oriented calculus uses a tuple variables i.e., variable whose only permitted values are tuples of that relation. E.g. QUEL The domain-oriented calculus has domain variables i.e.,...View answers

Questions : 25 :: What is Fully Functional dependency?

It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any...View answers

Questions : 26 :: What is 2NF

A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.

Questions : 27 :: What is 3NF?

A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true X is a Super-key of R. A is a prime attribute of R. In other words, if every non prime...View answers

Questions : 28 :: What is BCNF (Boyce-Codd Normal Form)?

A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key.

Questions : 29 :: What is meant by query optimization?

The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.

Questions : 30 :: What is durability in DBMS?

Once the DBMS informs the user that a transaction has successfully completed, its effects should persist even if the system crashes before all its changes are reflected on disk. This property is...View answers

Questions : 31 :: What do you mean by atomicity and aggregation?

Atomicity: Either all actions are carried out or none are. Users should not have to worry about the effect of incomplete transactions. DBMS ensures this by undoing the actions of incomplete...View answers

Questions : 32 :: What do you mean by flat file database?

It is a database in which there are no programs or user access languages. It has no cross-file capabilities but is user-friendly and provides user-interface management.

Questions : 33 :: What is "transparent DBMS"?

It is one, which keeps its Physical Structure hidden from user.

Questions : 34 :: What is a query?

A query with respect to DBMS relates to user commands that are used to interact with a data base. The query language can be classified into data definition language and data manipulation...View answers

Questions : 35 :: What do you mean by Correlated subquery?

Subqueries, or nested queries, are used to bring back a set of rows to be used by the parent query. Depending on how the subquery is written, it can be executed once for the parent query or it can be...View answers

Questions : 36 :: What is RDBMS KERNEL?

Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system-level data structures used by the kernel to manage the database...View answers

Questions : 37 :: Which part of the RDBMS takes care of the data dictionary? How?

Data dictionary is a set of tables and database objects that is stored in a special area of the database and maintained exclusively by the kernel.

Questions : 38 :: What is the job of the information stored in data-dictionary?

The information in the data dictionary validates the existence of the objects, provides access to them, and maps the actual physical storage location.

Questions : 39 :: How do you communicate with an RDBMS?

You communicate with an RDBMS using Structured Query Language (SQL).

Questions : 40 :: Define SQL and state the differences between SQL and other conventional programming Languages.

SQL is a nonprocedural language that is designed specifically for data access operations on normalized relational database structures. The primary difference between SQL and other conventional...View answers

Questions : 41 :: Name the three major set of files on disk that compose a database in Oracle.

There are three major sets of files on disk that compose a database. All the files are binary. These are 1.) Database files 2.) Control files3.) Redo logs The most important of these are the...View answers

Questions : 42 :: What is database Trigger?

A database trigger is a PL/SQL block that can defined to automatically execute for insert, update, and delete statements against a table. The trigger can e defined to execute once for the entire...View answers

Questions : 43 :: What are stored-procedures? And what are the advantages of using them?

Stored procedures are database objects that perform a user defined operation. A stored procedure can have a set of compound SQL statements. A stored procedure executes the SQL commands and returns...View answers

Questions : 44 :: What is Buffer Manager?

It is a program module, which is responsible for fetching data from disk storage into main memory and deciding what data to be cache in memory.

Questions : 45 :: What is Transaction Manager?

It is a program module, which ensures that database, remains in a consistent state despite system failures and concurrent transaction execution proceeds without conflicting.

Questions : 46 :: What is File Manager?

It is a program module, which manages the allocation of space on disk storage and data structure used to represent information stored on a disk.

Questions : 47 :: What is Authorization and Integrity manager?

It is the program module, which tests for the satisfaction of integrity constraint and checks the authority of user to access data.

Questions : 48 :: What are stand-alone procedures?

Procedures that are not part of a package are known as stand-alone because they independently defined. A good example of a stand-alone procedure is one written in a SQL*Forms application. These types...View answers

Questions : 49 :: What are cursors give different types of cursors?

PL/SQL uses cursors for all database information accesses statements. The language supports the use two types of cursors1.) Implicit2.)...View answers

Questions : 50 :: What is Storage Manager?

It is a program module that provides the interface between the low-level data stored in database, application programs and queries submitted to the system.

Questions : 51 :: What is cold backup and hot backup (in case of Oracle)?

Cold Backup: It is copying the three sets of files (database files, redo logs, and control file) when the instance is shut down. This is a straight file copy, usually from the disk directly to...View answers
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