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DBMS Interview Questions

A list of top frequently asked DBMS interview questions and answers are given below.

1) What is DBMS?

DBMS is a collection of programs that facilitates users to create and maintain a database.

2) What is a database?

Database is a logical, consistent and organized collection of data that it can easily be accessed, managed and updated.

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3) What is a database system?

The collection of database and DBMS software together is known as database system.

4) What are the advantages of DBMS?

Redundancy control
Restriction for unauthorized access
Provides multiple user interfaces
Provides backup and recovery
Enforces integrity constraints

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5) What is checkpoint in DBMS?

A Checkpoint is like a snapshot of the DBMS state.

6) When does checkpoint occur in DBMS?

By taking checkpoints, the DBMS can reduce the amount of work to be done during restart in the event of subsequent crashes.

7) What do you mean by transparent DBMS?

The transparent DBMS is a type of DBMS which keeps its physical structure hidden from users.

8) What are the unary operations in Relational Algebra?

PROJECTION and SELECTION are the unary operations in relational algebra.

9) How do you communicate with an RDBMS?

You have to use Structured Query Language (SQL) to communicate with RDBMS.

10) How many types of database languages are?

There are four types of database languages:

Data Definition Language (DDL) e.g. CREATE, ALTER, DROP etc.
Data Manipulation Language (DML) e.g. SELECT, UPDATE, INSERT etc.
DATA Control Language (DCL) e.g. GRANT and REVOKE.
Transaction Control Language (TCL) e.g. COMMIT and ROLLBACK.

11) What do you understand by Data Model?

Data model is specified as a collection of conceptual tools for describing data, data relationships data semantics and constraints.

12) Define a Relation Schema and a Relation.

A Relation Schema is denoted by R(A1, A2, ..., An) is made up of the relation name R and the list of attributes Ai that it contains.

A relation is specified as a set of tuples.

See this example:

Let r be the relation which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list of n-values t=(v1,v2, ..., vn).

13) What is degree of a Relation?

The degree of relation is a number of attribute of its relation schema.

14) What is Relationship?

Relationship is defined as an association among two or more entities.

15) What are the disadvantages of file processing systems?

Inconsistent
Not secure
Data redundancy
Difficult in accessing data
Data isolation
Data integrity
Concurrent access is not possible

16) What is data abstraction in DBMS?

Data abstraction in DBMS is a process of hiding irrelevant details from users. Because Database systems are made of complex data structures so, it makes easy the user interaction with database.

17) What are the three levels of data abstraction?

Following are three levels of data abstraction:

Physical level: It is the lowest level of abstraction. It describes how data are stored.

Logical level: It is the next higher level of abstraction. It describes what data are stored in database and what relationship among those data.

View level: It is the highest level of data abstraction. It describes only part of entire database.

18) What is DDL (Data Definition Language)?

Data Definition Language (DDL) is a standard for commands which define the different structures in a database. Most commonly DDL statements are CREATE, ALTER, and DROP.

19) What is DML (Data Manipulation Language)?

Data Manipulation Language (DML) is a language that enable user to access or manipulate data as organised by appropriate data model.

There are two type of DML:

Procedural DML or Low level DML: It requires a user to specify what data are needed and how to get those data.

Non-Procedural DML or High level DML: It requires a user to specify what data are needed without specifying how to get those data.

20) Explain the functionality of DML Compiler.

The DML Compiler translates DML statements in a query language that the query evaluation engine can understand.

21) What is Relational Algebra?

Relational Algebra is a Procedural Query Language which contains a set of operations that take one or two relations as input and produce a new relation.

22) What is Relational Calculus?

Relational Calculus is a Non-procedural Query Language which uses mathematical predicate calculus instead of algebra.

23) What do you understand by query optimization?

The term query optimization specifies an efficient execution plan for evaluating a query that has the least estimated cost.

24) What do you mean by 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 called durability.

25) What is normalization?

Normalization is a process of analyzing the given relation schemas according to their functional dependencies. It is used to minimize redundancy and also minimize insertion, deletion and update distractions.

26) What is Denormalization?

Denormalization is the process of boosting up database performance and adding of redundant data which helps to get rid of complex data.

27) What is functional Dependency?

Functional Dependency is the starting point of normalization. It exists when a relation between two attributes allows you to uniquely determine the corresponding attribute's value.

28) What is E-R model?

E-R model is a short name for Entity Relationship model. This model is based on real world. It contains basic objects (known as entities) and relationship among these objects.

29) What is entity?

Entity is a set of attributes in a database.

30) What is an Entity type?

An entity type is specified as a collection of entities, having same attributes.

31) What is an Entity set?

The entity set specifies the collection of all entities of particular entity type in the database.

32) What is an Extension of entity type?

An extension of entity type is specified as a collection of entities of a particular entity type are grouped together into an entity set.

33) What is Weak Entity set?

When an entity set doesn't have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is called Weak Entity set.

34) What is an attribute?

An attribute is a particular property, which describes the entity.

35) What are the integrity rules in DBMS?

There are two integrity rules in DBMS:

Entity Integrity: It specifies that "Primary key cannot have NULL value."

Referential Integrity: It specifies that "Foreign Key can be either a NULL value or should be Primary Key value of other relation.

36) What do you mean by extension and intension?

Extension: Extension is the number of tuples present in a table at any instance. This is time dependent.

Intension: Intension is a constant value that gives the name, structure of table and the constraints laid on it.

37) What is System R? How many of 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 which is developed to demonstrate that it is possible to build a Relational System that can be used in a real life environment to solve real life problems, with performance at least comparable to that of existing system.

Following are two major subsystems of System R:

Research Storage
System Relational Data System

38) What is Data Independence?

Data independence specifies that "the application is independent of the storage structure and access strategy of data".

It makes you able to modify the schema definition in one level should not affect the schema definition in the next higher level.

There are two types of Data Independence:

Physical Data Independence: Modification in physical level should not affect the logical level.

Logical Data Independence: Modification in logical level should affect the view level.

NOTE: Logical Data Independence is more difficult to achieve.

39) What are the three levels of data abstraction?

Physical level: It is the lowest level of abstraction. It describes how data are stored.

Logical level: It is the next higher level of abstraction. It describes what data are stored in database and what relationship among those data.

View level: It is the highest level of abstraction. It describes only part of entire database.

40) What is stored procedure?

A stored procedure is a named group of SQL statements that have been previously created and stored in the server database.

41) What is 1NF?

1NF is the First Normal Form. It is the simplest type of normalization that you can implement in a database. The main objectives of 1NF are to:

Remove duplicate columns from the same table
Create separate tables for each group of related data and identify each row with a unique column

42) What is 2NF?

2NF is the Second Normal Form. A table is said to be 2NF, if it follows the following conditions:

The table is in 1NF.
Every non-prime attribute is fully functionally dependent on primary key.

43) What is 3NF?

3NF stands for Third Normal Form. A database is called in 3NF if satisfies the following conditions:

It is in second normal form.
There is no transitive functional dependency.

44) What is BCNF?

BCMF stands for Boyce-Codd Normal Form. It is an advance version of 3NF so it is also referred as 3.5NF. BCNF is stricter than 3NF.

A table complies with BCNF if it satisfies the following conditions:

It is in 3NF.
For every functional dependency X->Y, X should be the super key of the table.

SQL Interview Questions

There is given sql interview questions and answers that has been asked in many companies. For PL/SQL interview questions, visit our next page.

1) What is SQL?

SQL stands for structured query language. It is a database language used for database creation, deletion, fetching rows and modifying rows etc. sometimes it is pronounced as se-qwell.

2) When SQL appeared?

It appeared in 1974.

3) What are the usages of SQL?

To execute queries against a database
To retrieve data from a database
To inserts records in a database
To updates records in a database
To delete records from a database
To create new databases
To create new tables in a database
To create views in a database

4) Does SQL support programming?

No, SQL doesn't have loop or Conditional statement. It is used like commanding language to access databases.

5) What are the subsets of SQL?

1. Data definition language (DDL)

2. Data manipulation language (DML)

3. Data control language (DCL)

6) What is data definition language?

Data definition language(DDL) allows you to CREATE, ALTER and DELETE database objects such as schema, tables, view, sequence etc.

7) What is data manipulation language?

Data manipulation language makes user able to access and manipulate data. It is used to perform following operations.

Insert data into database
Retrieve data from the database
Update data in the database
Delete data from the database

8) What is data control language?

Data control language allows you to control access to the database. It includes two commands GRANT and REVOKE.

GRANT: to grant specific user to perform specific task.

REVOKE: to cancel previously denied or granted permissions.

9) What are tables and fields in database?

A table is a set of organized data. It has columns and rows. Columns can be categorized as vertical, and Rows are horizontal.

A table contains specified number of column called fields but can have any number of rows which is known as record.

10) What is a primary key?

A primary key is a combination of fields which uniquely specify a row. This is a special kind of unique key. Primary key values cannot be NULL.

11) What is a foreign key?

A foreign key is specified as a key which is related to the primary key of another table. Relationship needs to be created between two tables by referencing foreign key with the primary key of another table.

12) What is a unique key?

A Unique key constraint uniquely identifies each record in the database. This provides uniqueness for the column or set of columns.

13) What are the type of operators available in SQL?

1. Arithmetic operators

2. Logical operators

3. Comparison operator

14) What is view in SQL?

A view is a virtual table which contains a subset of data within a table. Views are not virtually present, and it takes less space to store. View can have data of one or more tables combined, and it is depending on the relationship.

15) What is an Index in SQL?

Index is used to increase the performance and allow faster retrieval of records from the table. An index creates an entry for each value and it will be faster to retrieve data.

16) Which are the different types of indexes in SQL?

There are three types of Indexes in SQL:

Unique Index
Clustered Index
NonClustered Index

17) What is Unique Index?

Unique Index:

This indexing does not allow the field to have duplicate values if the column is unique indexed. Unique index can be applied automatically when primary key is defined.

18) What is Clustered Index in SQl?

Clustered Index:

The clustered index is used to reorder the physical order of the table and search based on the key values. Each table can have only one clustered index.

19) What is NonClustered Index in SQL?

NonClustered Index:

NonClustered Index does not alter the physical order of the table and maintains logical order of data. Each table can have 999 non-clustered indexes.

20) What is the difference between SQL, MySQL and SQL Server?

SQL or Structured Query Language is a language which is used to communicate with a relational database. It provides a way to manipulate and create databases. On the other hand, MySQL and Microsoft's SQL Server both are relational database management systems that use SQL as their standard relational database language.

21) What is the difference between SQL and PL/SQL?

SQL or Structured Query Language is a language which is used to communicate with a relational database. It provides a way to manipulate and create databases. On the other hand, PL/SQL is a dialect of SQL which is used to enhance the capabilities of SQL. It was developed by Oracle Corporation in the early 90's. It adds procedural features of programming languages in SQL.

22) Is it possible to sort a column using a column alias?

Yes. You can use column alias in the ORDER BY clause for sorting.

23) What is the difference between clustered and non clustered index in SQL?

There are mainly two type of indexes in SQL, Clustered index and non clustered index. The differences between these two indexes is very important from SQL performance perspective.

1. One table can have only one clustered index but it can have many non clustered index.(approximately 250).

2. clustered index determines how data is stored physically in table. Actually clustered index stores data in cluster, related data is stored together so it makes simple to retrieve data.

3. reading from a clustered index is much faster than reading from non clustered index from the same table.

4. clustered index sort and store data rows in the table or view based on their key value, while non cluster have a structure separate from the data row.

24) What is the SQL query to display current date?

There is a built in function in SQL called GetDate() which is used to return current timestamp.

25) Which are the most commonly used SQL joins?

Most commonly used SQL joins are INNER JOIN and (left/right) OUTER JOIN.

26) What are the different types of joins in SQL?

Joins are used to merge two tables or retrieve data from tables. It depends on the relationship between tables.

Following are the most commonly used joins in SQL:

Inner Join
Right Join
Left Join
Full Join

27) What is Inner Join in SQL?

Inner join:

Inner join returns rows when there is at least one match of rows between the tables.

28) What is Right Join in SQL?

Right Join:

Right join is used to retrieve rows which are common between the tables and all rows of Right hand side table. It returns all the rows from the right hand side table even though there are no matches in the left hand side table.

29) What is Left Join in SQL?

Left Join:

Left join is used to retrieve rows which are common between the tables and all rows of Left hand side table. It returns all the rows from Left hand side table even though there are no matches in the Right hand side table.

30) What is Full Join in SQL?

Full Join:

Full join return rows when there are matching rows in any one of the tables. This means, it returns all the rows from the left hand side table and all the rows from the right hand side table.

31) What is "TRIGGER" in SQL?

Trigger allows you to execute a batch of SQL code when an insert, update or delete command is executed against a specific table.

Actually triggers are special type of stored procedures that are defined to execute automatically in place or after data modifications.

32) What is self join and what is the requirement of self join?

Self join is often very useful to convert a hierarchical structure to a flat structure. It is used to join a table to itself as like if that is the second table.

33) What are set operators in SQL?

Union, Intersect or Minus operators are called set operators.

34) What is the difference between BETWEEN and IN condition operators?

The BETWEEN operator is used to display rows based on a range of values. The IN condition operator is used to check for values contained in a specific set of values.

35) What is a constraint? Tell me about its various levels.

Constraints are representators of a column to enforce data entity and consistency. There are two levels :

1. column level constraint

2. table level constraint

36) Write an SQL query to find names of employee start with 'A'?

1. SELECT * FROM Employees WHERE EmpName like 'A%'

37) Write an SQL query to get third maximum salary of an employee from a table named employee_table.

1. SELECT TOP 1 salary

2. FROM (

3. SELECT TOP 3 salary

4. FROM employee_table

5. ORDER BY salary DESC ) AS emp

6. ORDER BY salary ASC;

38) What is the difference between DELETE and TRUNCATE statement in SQL?

The main differences between SQL DELETE and TRUNCATE statements are given below:

No.	DELETE	TRUNCATE
1)	DELETE is a DML command.	TRUNCATE is a DDL command.
2)	We can use WHERE clause in DELETE command.	We cannot use WHERE clause with TRUNCATE
3)	DELETE statement is used to delete a row from a table	TRUNCATE statement is used to remove all the rows from a table.
4)	DELETE is slower than TRUNCATE statement.	TRUNCATE statement is faster than DELETE statement.
5)	You can rollback data after using DELETE statement.	It is not possible to rollback after using TRUNCATE statement.

39) What is ACID property in database?

ACID property is used to ensure that the data transactions are processed reliably in a database system.

A single logical operation of a data is called transaction.

ACID is an acronym for Atomicity, Consistency, Isolation, Durability.

Atomicity: it requires that each transaction is all or nothing. It means if one part of the transaction fails, the entire transaction fails and the database state is left unchanged.

Consistency: the consistency property ensure that the data must meet all validation rules. In simple words you can say that your transaction never leaves your database without completing its state.

Isolation: this property ensure that the concurrent property of execution should not be met. The main goal of providing isolation is concurrency control.

Durability: durability simply means that once a transaction has been committed, it will remain so, come what may even power loss, crashes or errors.

40) What is the difference among NULL value, zero and blank space?

Ans: A NULL value is not same as zero or a blank space. A NULL value is a value which is 'unavailable, unassigned, unknown or not applicable'. On the other hand, zero is a number and blank space is treated as a character.

41) What is the usage of SQL functions?

SQL functions are used for following purpose:

To perform calculations on data.
To modify individual data items.
To manipulate the output.
To format dates and numbers.
To convert data types.

42) Which are the different case manipulation functions in SQL?

There are three case manipulation functions in SQL:

LOWER
UPPER
INITCAP

43) What is the usage of NVL function?

The NVL function is used to convert NULL value to a actual value.

44) Which function is used to return remainder in a division operator in SQL?

The MOD function returns the remainder in a division operation.

45) What is the syntax and use of the COALESCE function?

The syntax of COALESCE function:

1. COALESCE(exp1, exp2, ... expn)

The COALESCE function is used to return the first non-null expression given in the parameter list.

46) What is the usage of DISTINCT keyword?

The DISTINCT keyword is used to ensure that the fetched value is only a non-duplicate value.

PL/SQL Interview Questions

PL/SQL is an advance version of SQL. There are given top list of PL/SQL interview questions with answer.

1) What is PL/SQL?

PL/SQL stands for procedural language extension to SQL. It supports procedural features of programming language and SQL both. It was developed by Oracle Corporation in early of 90's to enhance the capabilities of SQL.

2) What is the purpose of using PL/SQL?

PL/SQL is an extension of SQL. While SQL is non-procedural, PL/SQL is a procedural language designed by Oracle. It is invented to overcome the limitations of SQL.

3) What are the most important characteristics of PL/SQL?

A list of some notable characteristics:

PL/SQL is a block-structured language.
It is portable to all environments that support Oracle.
PL/SQL is integrated with the Oracle data dictionary.
Stored procedures help better sharing of application.

4) What is PL/SQL table? Why it is used?

Objects of type tables are called PL/SQL tables that are modeled as database table. We can also say that PL/SQL tables are a way to providing arrays. Arrays are like temporary tables in memory that are processed very quickly. PL/SQL tables are used to move bulk data. They simplifies moving collections of data.

5) What are the datatypes available in PL/SQL?

There are two types of datatypes in PL/SQL:

1. Scalar datatypes Example are NUMBER, VARCHAR2, DATE, CHAR, LONG, BOOLEAN etc.

2. Composite datatypes Example are RECORD, TABLE etc.

6) What is the basic structure of PL/SQL?

PL/SQL uses BLOCK structure as its basic structure. Each PL/SQL program consists of SQL and PL/SQL statement which form a PL/SQL block.

PL/SQL block contains 3 sections.

1. The Declaration Section (optional)

2. The Execution Section (mandatory)

3. The Exception handling Section (optional)

7) What is the difference between FUNCTION, PROCEDURE AND PACKAGE in PL/SQL?

Function: The main purpose of a PL/SQL function is generally to compute and return a single value. A function has a return type in its specification and must return a value specified in that type.

Procedure: A procedure does not have a return type and should not return any value but it can have a return statement that simply stops its execution and returns to the caller. A procedure is used to return multiple values otherwise it is generally similar to a function.

Package: A package is schema object which groups logically related PL/SQL types , items and subprograms. You can also say that it is a group of functions, procedure, variables and record type statement. It provides modularity, due to this facility it aids application development. It is used to hide information from unauthorized users.

8) What is exception? What are the types of exceptions?

Exception is an error handling part of PL/SQL. There are two type of exceptions: pre_defined exception and user_defined exception.

9) How to write a single statement that concatenates the words ?Hello? and ?World? and assign it in a variable named Greeting?

Greeting := 'Hello' || 'World';

10) Does PL/SQL support CREATE command?

No. PL/SQL doesn't support the data definition commands like CREATE.

11) Write a unique difference between a function and a stored procedure.

A function returns a value while a stored procedure doesn?t return a value.

12) How exception is different from error?

Whenever an Error occurs Exception arises. Error is a bug whereas exception is a warning or error condition.

13) What is the main reason behind using an index?

Faster access of data blocks in the table.

14) What are PL/SQL exceptions? Tell me any three.

1. Too_many_rows

2. No_Data_Found

3. Value_error

4. Zero_error etc.

15) How do you declare a user-defined exception?

You can declare the User defined exceptions under the DECLARE section, with the keyword EXCEPTION.

Syntax:

1. <exception_name> EXCEPTION;

16) What are some predefined exceptions in PL/SQL?

A list of predefined exceptions in PL/SQL:

DUP_VAL_ON_INDEX
ZERO_DIVIDE
NO_DATA_FOUND
TOO_MANY_ROWS
CURSOR_ALREADY_OPEN
INVALID_NUMBER
INVALID_CURSOR
PROGRAM_ERROR
TIMEOUT _ON_RESOURCE
STORAGE_ERROR
LOGON_DENIED
VALUE_ERROR
etc.

17) What is a trigger in PL/SQL?

A trigger is a PL/SQL program which is stored in the database. It is executed immediately before or after the execution of INSERT, UPDATE, and DELETE commands.

18) What is the maximum number of triggers, you can apply on a single table?

12 triggers.

19) How many types of triggers exist in PL/SQL?

There are 12 types of triggers in PL/SQL that contains the combination of BEFORE, AFTER, ROW, TABLE, INSERT, UPDATE, DELETE and ALL keywords.

BEFORE ALL ROW INSERT
AFTER ALL ROW INSERT
BEFORE INSERT
AFTER INSERT etc.

20) What is the difference between execution of triggers and stored procedures?

A trigger is automatically executed without any action required by the user, while, a stored procedure is explicitly invoked by the user.

21) What happens when a trigger is associated to a view?

When a trigger is associated to a view, the base table triggers are normally enabled.

22) What is the usage of WHEN clause in trigger?

A WHEN clause specifies the condition that must be true for the trigger to be triggered.

23) How to disable a trigger name update_salary?

ALTER TRIGGER update_salary DISABLE;

24) Which command is used to delete a trigger?

DROP TRIGGER command.

25) what are the two virtual tables available at the time of database trigger execution?

Table columns are referred as THEN.column_name and NOW.column_name.

For INSERT related triggers, NOW.column_name values are available only.

For DELETE related triggers, THEN.column_name values are available only.

For UPDATE related triggers, both Table columns are available.

26) What is stored Procedure?

A stored procedure is a sequence of statement or a named PL/SQL block which performs one or more specific functions. It is similar to a procedure in other programming languages. It is stored in the database and can be repeatedly executed. It is stored as schema object. It can be nested, invoked and parameterized.

27) What are the different schemas objects that can be created using PL/SQL?

Stored procedures and functions
Packages
Triggers
Cursors

28) What do you know by PL/SQL Cursors?

Oracle uses workspaces to execute the SQL commands. When Oracle processes a SQL command, it opens an area in the memory called Private SQL Area. This area is identified by the cursor. It allows programmers to name this area and access it?s information.

29) What is the difference between the implicit and explicit cursors?

Implicit cursor is implicitly declared by Oracle. This is a cursor to all the DDL and DML commands that return only one row.

Explicit cursor is created for queries returning multiple rows.

30) What will you get by the cursor attribute SQL%ROWCOUNT?

The cursor attribute SQL%ROWCOUNT will return the number of rows that are processed by a SQL statement.

31) What will you get by the cursor attribute SQL%FOUND?

It returns the Boolean value TRUE if at least one row was processed.

32) What will you get by the cursor attribute SQL%NOTFOUND?

It returns the Boolean value TRUE if no rows were processed.

33) What do you understand by PL/SQL packages?

A PL/SQL package can be specified as a file that groups functions, cursors, stored procedures, and variables in one place.

34) What are the two different parts of the PL/SQL packages?

PL/SQL packages have the following two parts:

Specification part: It specifies the part where the interface to the application is defined.

Body part: This part specifies where the implementation of the specification is defined.

35) Which command is used to delete a package?

The DROP PACKAGE command is used to delete a package.

36) How to execute a stored procedure?

There are two way to execute a stored procedure.

From the SQL prompt, write EXECUTE or EXEC followed by procedure_name.

1. EXECUTE or [EXEC] procedure_name;

Simply use the procedure name

1. procedure_name;

37) What are the advantages of stored procedure?

Modularity, extensibility, reusability, Maintainability and one time compilation.

38) What are the cursor attributes used in PL/SQL?

%ISOPEN: it checks whether the cursor is open or not.

%ROWCOUNT: returns the number of rows affected by DML operations: INSERT,DELETE,UPDATE,SELECT.

%FOUND: it checks whether cursor has fetched any row. If yes - TRUE.

%NOTFOUND: it checks whether cursor has fetched any row. If no - TRUE.

39) What is the difference between syntax error and runtime error?

A syntax error can be easily detected by a PL/SQL compiler. For example: incorrect spelling etc. while, a runtime error is handled with the help of exception-handling section in a PL/SQL block. For example: SELECT INTO statement, which does not return any rows.

40) Explain the Commit statement.

Following conditions are true for the Commit statement:

Other users can see the data changes made by the transaction.
The locks acquired by the transaction are released.
The work done by the transaction becomes permanent.

41) Explain the Rollback statement?

The Rollback statement is issued when the transaction ends. Following conditions are true for a Rollback statement:

The work done in a transition is undone as if it was never issued.
All locks acquired by transaction are released.

42) Explain the SAVEPOINT statement.

With SAVEPOINT, only part of transaction can be undone.

43) What is mutating table error?

Mutating table error is occurred when a trigger tries to update a row that it is currently using. It is fixed by using views or temporary tables.

44) What is consistency?

Consistency simply means that each user sees the consistent view of the data.

Consider an example: there are two users A and B. A transfers money to B's account. Here the changes are updated in A's account (debit) but until it will be updated to B's account (credit), till then other users can't see the debit of A's account. After the debit of A and credit of B, one can see the updates. That?s consistency.

45) What is cursor and why it is required?

A cursor is a temporary work area created in a system memory when an SQL statement is executed.

A cursor contains information on a select statement and the row of data accessed by it. This temporary work area stores the data retrieved from the database and manipulate this data. A cursor can hold more than one row, but can process only one row at a time. Cursor are required to process rows individually for queries.

46) How many types of cursors are available in PL/SQL?

There are two types of cursors in PL/SQL.

1. Implicit cursor, and

2. explicit cursor

Data Structure Interview Questions

A list of top frequently asked Data Structure interview questions and answers are given below.

1) What is Data Structure? Explain.

Data structure is a way that specifies how to organize and manipulate the data. It also specifies the relationship between them. It provides some algorithms to make data access more efficient and easy.

2) In which areas data structures are applied extensively?

Data structures are applied extensively in the following areas of computer science:

Compiler Design,
Operating System,
Database Management System,
Statistical analysis package,
Numerical Analysis,
Graphics,
Artificial Intelligence,
Simulation

3) What is the difference between file structure and storage structure?

Difference between file structure and storage structure:

The main difference between file structure and storage structure is based on memory area that is being accessed.

Storage structure: When we deal with the structure that resides in the main memory of the computer system, known as the storage structure.

File structure: When we deal with an auxiliary structure then it is referred as file structures.

4) Which data structures are used with the following areas: RDBMS, Network data model and hierarchical data model?

RDBMS uses Array data structure
Network data model uses Graph
Hierarchal data model uses Trees

5) What are Binary trees?

A Binary Tree is a type of data structure that has two nodes: A left node and a right node. In programming, binary trees are actually an extension of the linked list structures.

6) What is a Stack?

A stack is a data structure in which only the top element can be accessed. As data is stored in the stack, each data is pushed downward, leaving the most recently added data on top.

7) What is a multidimensional array?

A multidimensional array stores data in multiple indexes. It is used when the storing data that cannot be represented using a single dimensional indexing, such as data representation in a board game, tables with data stored in more than one column.

8) What is a linked list in data structure?

A linked list is a sequence of nodes in which each node is connected to the node following it. It makes a chain like link of data storage.

9) If you are using C language to implement the heterogeneous linked list, what pointer type should be used?

The heterogeneous linked list contains different data types, so it is not possible to use ordinary pointers for this. For this work, you have to use a generic pointer type like void pointer because void pointer is capable of storing pointer to any type.

10) How many minimum numbers of queues are needed to implement the priority queue?

Two queues are needed. One queue is used for actual storing of data and another for storing priorities.

11) Which data structure is used to perform recursion?

Stack is used to perform recursion because of its LIFO (Last In First Out) property. It knows whom to return when the function has to return.

12) When should you use binary search engine?

A binary search algorithm is used to search a list when the elements are already in order or sorted. The list starts searching in the middle, if the middle value is not the target search key, it will check to see if it will continue the search on the lower half of the list or the higher half. The split and search will then continue in the same manner.

Example:

13) How to reference all the elements in a one-dimension array?

It can be done by using an indexed loop such that the counter runs from 0 to the array size minus one. By this manner, you can reference all the elements in sequence by using the loop counter as the array subscript.

14) Which notations are used in Evaluation of Arithmetic Expressions using prefix and postfix forms?

Polish and Reverse Polish notations.

15) Give some example of the application of Tree-data structure?

Application of Tree- data structure:

The manipulation of Arithmetic expression,
Symbol Table construction,
Syntax analysis

16) Give the example of some applications that make use of Multilinked Structures?

Sparse matrix,
Index generation.

17) Are linked lists considered linear or non-linear data structures?

A linked list is considered both linear and non-linear data structure depending on the situation.

On the basis of data storage, it is considered as non-linear data structure.
On the basis of access strategy, it is considered as linear data-structure.

18) What is the difference between NULL and VOID?

Null is actually a value, whereas Void is a data type identifier.
A null variable simply indicates an empty value, whereas void is used to identify pointers as having no initial size.

19) What is the difference between PUSH and POP?

PUSH and POP operations specify how data is stored and retrieved in a stack.

PUSH: PUSH specifies that data is being "pushed" into the stack.

POP: POP specifies data retrieval, and in particular refers to the topmost data being accessed.

20) What is a postfix expression?

An expression which each operator follows its operand is known as postfix expression. The main benefit of this form is that there is no need to group sub-expressions in parentheses or to consider operator precedence.

Linux Interview Questions

A list of top frequently asked Linux interview questions and answers are given below.

1) What is Linux?

Linux is a UNIX based operating system. It was first introduced by Linus Torvalds. It is an open source operating system that was designed to provide free and a low cost operating system for the computer users.

2) What is the difference between UNIX and Linux?

UNIX was originally started as a propriety operating system for Bell laboratories, which later release their commercial version while Linux is a free, open source and a non propriety operating system for the mass uses.

3) What is Linux Kernel?

Linux Kernel is low level system software. It is used to manage the hardware resources for the users. It provides an interface for user-level interaction.

4) Is it legal to edit Linux Kernel?

Yes. You can edit Linux Kernel because it is released under General Public License (GPL) and any one can edit it. It comes under the category of free and open source software.

5) What is LILO?

LILO is a boot loader for Linux. It is used to load the Linux operating system into the main memory to begin its operations.

6) What is the advantage of open source?

Open source facilitates you to distribute your software, including source codes freely to anyone who is interested. So, you can add features and even debug and correct errors of the source code.

7) What are the basic components of Linux?

Just like other operating systems, Linux has all components like kernel, shells, GUIs, system utilities and application programs.

8) What is the advantage of Linux?

Every aspect comes with additional features and it provides a free downloading facility for all codes.

9) What is Swap Space?

Swap space is used to specify a space which is used by Linux to hold some concurrent running program temporarily. It is used when RAM does not have enough space to hold all programs that are executing.

10) What is BASH?

BASH is a short form of Bourne Again SHell. It was a replacement to the original Bourne shell, written bu Steve Bourne.

11) What is the basic difference between BASH and DOS?

BASH commands are case sensitive while DOS commands are not case sensitive.
DOS follows a convention in naming files. In DOS, 8 character file name is followed by a dot and 3 characters for the extension. BASH doesn't follow such convention.

12) What is a root account?

The root account is like a system administrator account. It provides you full control of the system. You can create and maintain user accounts, assign different permission for each account etc.

13) What is CLI?

CLI stands for Command Line Interface. It is an interface that allows users to type declarative commands to instruct the computer to perform operations.

14) What is GUI?

GUI stands for Graphical User Interface. It uses the images and the icons which are clicked by the users to communicate with the system. It is more attractive and user-friendly because the use of the images and icons.

15) Which popular office suite is available free for both Microsoft and Linux?

Open Office Suite is available free for both Microsoft and Linux. You can install it on both of them.

16) Suppose your company is recently switched from Microsoft to Linux and you have some MS Word document to save and work in Linux, what will you do?

Install Open Office Suite on Linux. It facilitates you to work with Microsoft documents.

17) What is SMTP?

SMTP stands for Simple Mail Transfer Protocol. It is an internet standard for mail transmission.

18) What is Samba? Why is it used?

Samba service is used to connect Linux machines to Microsoft network resources by providing Microsoft SMB support.

19) What are the basic commands for user management?

last,
chage,
chsh,
lsof,
chown,
chmod,
useradd,
userdel,
newusers etc.

20) What is the maximum length for a file name in Linux?

255 characters.

21) Is Linux Operating system virus free?

No, There is no operating system till date that is virus free but Linux is known to have less number of viruses.

22) Which partition stores the system configuration files in Linux system?

/stc partition.

23) Which command is used to uncompress gzip files?

gunzip command is used to uncompress gzip files.

24) Why do developers use MD5 options on passwords?

MD5 is an encryption method so it is used to encrypt the passwords before saving.

25) What is a virtual desktop?

The virtual desktop is used as an alternative to minimizing and maximizing different windows on the current desktop. Virtual desktop facilitates you to open one or more programs on a clean slate rather than minimizing or restoring all the needed programs.

26) What is the difference between soft and hard mounting points?

In the soft mount, if the client fails to connect the server, it gives an error report and closes the connection whereas in hard mount, if the client fails to access the server, the connection hangs; and once the system is up, it again accesses the server.

27) Does the Alt+Ctrl+Del key combination work in Linux?

Yes, it works like windows.

28) What are the file permissions in Linux?

There are 3 types of permissions in Linux OS that are given below:

Read: User can re

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