300+ [UPDATED] DBMS+RDBMS Interview Questions

1. What Is Database Or Database Management Systems (dbms)?

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.

2. 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 purpose.

3. 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.

4. Can You Explain The Between Clause In Dbms?

Below SQL selects employees born between ’01/01/1995′ AND ’01/01/1978′ as per mysql

SELECT * FROM wbEmployee WHERE DOB BETWEEN ‘1995-01-01’ AND ‘2011-09-28’

5. What Is An Attribute?

It is a particular property, which describes the entity.

6. 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.

7. What’s The Difference Between File And Database? Can Files Qualify As A Database?

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.

8. What Is A Database System?

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

9. 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 distractio

10. What Is The Sql ” In ” Clause?

SQL IN operator is used to see if the value exists in a group of values. For instance the below

SQL checks if the Name is either ‘David’ or ‘Craig’ SELECT * FROM wbEmployee WHERE name IN (‘David’,’Craig’) Also you can specify a not clause with the same. SELECT * FROM wbEmployee WHERE age NOT IN (30,25)

11. What Is Weak Entity Set?

An entity set may not 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 said to be Weak Entity set.

12. What Is Data Independence?

Data independence specifies that the application is independent of the storage structure and the access strategy of data. It means the ability 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
• Logical data independence

13. What Is Sql?

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.

14. What Are The Advantages Of Dbms?

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

15. 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.

16. What Is Order By Clause In Dmbs?

ORDER BY clause helps to sort the data in either ascending order to descending order.

• Ascending order sort query : 
  SELECT name,age FROM pcdsEmployee ORDER BY age ASC.
• Descending order sort query : 
  SELECT name FROM pcdsEmployee ORDER BY age DESC.

17. What Is An Extension Of Entity Type?

The collections of entities of a particular entity type are grouped together into an entity set.

18. What Is Entity?

Entity is a set of attributes in a database.

19. What’s Difference Between Dbms And Rdbms?

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.

20. 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 Problems.

21. 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.

22. Can You Explain Insert, Update And Delete Query In Dbms?

Insert statement is used to insert new rows in to table. Update to update existing data in the table. Delete statement to delete a record from the table. Below code snippet for Insert, Update and Delete :-

INSERT INTO wbEmployee SET name=’maxwell’,age=’22’;
UPDATE wbEmployee SET age=’22’ where name=’maxwell’;
DELETE FROM wbEmployee WHERE name = ‘david’;

23. What Is An Entity Set?

It is a collection of all entities of particular entity type in the database.

24. 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.

25. How Many Types Of Relationship Exist In Database Designing?

There are three major relationship models:-

• One-to-one
• One-to-many
• Many-to-many

26. 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 on it.

27. Why A Database Is Called As Relational Database Model?

A database model represents the relationship between one or more databases. The relationship is known as the relational database model. It is an extension of the normal databases without relations. It provides flexibility and allows one database to be in relation with another database. It can access the data from many databases at one time over the network.

28. What Are Entities And Attributes Referring To?

Table consists of some properties that are known as attributes. These consist of the representation of entity in the table. They are represented by columns in the table. Entity is referred to the store data about any particular thing. It is the smallest unit inside the table.

29. What Do You Understand By Relation In Relational Database Model?

Relation in the relational database model is defined as the set of tuples that have the same attributes. Tuple represents an object and also the information that the object contains. Objects are basically instances of classes and used to hold the larger picture. Relation is described as a table and is organized in rows and columns. The data referenced by the relation come in the same domain and have the same constraints as well. Relations in the relational database model can be modified using the commands like insert, delete etc.

30. Why Domain Is Of High Importance?

Domain describes possible values grouped together that can be given for an attribute. It is considered the same way as a constraint on the value of attribute. A domain can be attached to an attribute but only if the attribute is an element of specified set. For example: XYZ doesn’t fulfill the domain constraint but the integer value as 899 fulfills the criteria of domain constraint. Hence, domain is of high importance.

31. Advantages Of Dbms?

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

32. What Is The Difference Between Base And Derived Relation?

Relational database means the relationship between different databases. In relational database user can store and access all the data through the tables which are related to each other. Relationship between the store data is called base relations and implementation of it is called as tables. Whereas, relations which don’t store the data, but can be found out by applying relational operations on other relations are called as derived relations. When these are implemented they are termed as views or queries. Derived relations are more useful then base relation, as they can have more information from many relations, but they act as a single relation.

33. Disadvantage In File Processing System?

• Data redundancy & inconsistency.
• Difficult in accessing data.
• Data isolation.
• Data integrity.
• Concurrent access is not possible.
• Security Problems.

34. What Are Constraints In Database?

Constraints are kind of restrictions that are applied to the database or on the domain of an attribute. For example an integer attribute is restricted from 1-10 and not more than that. They provide the way to implement the business logic and the rules in database. In database it can be implemented in the form of check constraints that checks for the rules that haven’t been followed by the programmer. Constraint also used to restrict the data that can be stored in the relations. Domain constraint can be applied to check the domain functionality and keep it safe..

35. 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 stored in database and what relationship among those data.
• View level:
  The highest level of abstraction describes only part of entire database.

36. What Are The Two Principles Of Relational Database Model? What Is The Difference Between Them?

The two principal rules for the relational model are as follows:

1. Entity integrity:
   this is used to maintain the integrity at entity level
2. Referential integrity:
   it is used to maintain integrity on all the values which have been referenced.

The differences between them are as follows:

• Entity integrity tells that in a database every entity should have a unique key; on the other hand referential integrity tells that in the database every table values for all foreign keys will remain valid.
• Referential integrity is based on entity integrity but it is not the other way around.

For example:
if a table is present and there is a set of column out of which one column has parent key set then to ensure that the table doesn’t contain any duplicate values, a unique index is defined on the column that contains the parent key.

37. Define The Integrity Rules?

There are two Integrity rules.

1. Entity Integrity:
   States that Primary key cannot have NULL value
2. Referential Integrity:
   States that Foreign Key can be either a NULL value or should be Primary Key value of other relation.

38. What Is The Difference Between Primary And Foreign Key?

• Primary key uniquely identify a relationship in a database, whereas foreign key is the key that is in other relation and it has been referenced from the primary key from other table.
• Primary key remains one only for the table, whereas there can be more than one foreign key.
• Primary key is unique and won’t be shared between many tables, but foreign key will be shared between more than one table and will be used to tell the relationship between them.

39. Why Stored Procedures Are Called As Executable Code?

Stored procedure stored inside the database. This also includes the executable code that usually collects and customizes the operations like insert, encapsulation, etc. These stored procedures are used as APIs for simplicity and security purposes. The implementation of it allows the developers to have procedural extensions to the standard SQL syntax. Stored procedure doesn’t come as a part of relational database model, but can be included in many implementations commercially.

40. 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 that can be used in a real life environment to solve real life problems, with performance at least comparable to that of existing system.
Its two subsystems are

• Research Storage
• System Relational Data System.

41. What Is An Index Represent In Relational Database Model?

Index is a way to provide quick access to the data and structure. It has indexes maintain and can be created to combine attributes on a relation. Index allows the queries to filter out the searches faster and matching data can be found earlier with simplicity. For example it is same as the book where by using the index you can directly jump to a defined section. In relational database there is a provision to give multiple indexing techniques to optimize the data distribution.

42. 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 enforced

43. What Are The Relational Operations That Can Be Performed On The Database?

There are many relational operators that are used to perform actions on relational database. These operators are as follows:

• union operator:
  that combines the rows of two relations and doesn’t include any duplicate. It also removes the duplicates from the result.
• intersection operator:
  provides a set of rows that two relations have in common.
• difference operator:
  provide the output by taking two relations and producing the difference of rows from first that don’t exist in second.
• cartesian product:
  is done on two relations. It acts as a cross join operator.

44. What Do You Understand By Database Normalization?

Normalization is very essential part of relational model. It consists of set of procedures that eliminates the domains that are non-atomic and redundancy of data that prevents data manipulation and loss of data integrity. Normal forms are the common form of normalization. It helps in reducing redundancy to increase the information overall. It has some disadvantages as it increases complexity and have some overhead of processing.

45. 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 stored file that direct represents the view instead a definition of view is stored in data dictionary.

Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.

46. What Is Data Model?

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

47. How De-normalization Is Different From Normalization?

Analytical processing databases are not very normalized. The operations which are used are read most databases. It is used to extract the data that are ancient and accumulated over long period of time. For this purpose de-normalization occurs that provide smart business applications. Dimensional tables in star schema are good example of de-normalized data. The de-normalized form must be controlled while extracting, transforming, loading and processing. There should be constraint that user should not be allowed to view the state till it is consistent. It is used to increase the performance on many systems without RDBMS platform.

48. What Is The Type Of De-normalization?

Non-first normal form (NFA) – it describes the definition of the database design which is different from the first normal form. It keeps the values in structured and specialized types with their own domain specific languages. The query language used in this is extended to incorporate more support for relational domain values by adding more operators.

49. 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 bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.

50. How Many Levels Of Data Abstraction Present?

There are three levels of data abstraction that is present in database model and these are as follows:

• physical level:
  it is the lowest level that describes how data is stored inside the database.
• logical level:
  it is the next higher level in the hierarchy that provides the abstraction. It describes what data are stored and the relationship between them.
• view level :
  it is the highest level in hierarch that describes part of the entire database. It allows user to view the database and do the query.

51. What Is An Entity Type?

It is a collection (set) of entities that have same attributes.

52. 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.

53. What Is Sdl (storage Definition Language)?

This language is to specify the internal schema. This language may specify the mapping between two schemas.

54. What Is The Difference Between Dbms And Rdbms?

• DBMS is persistent and accessible when the data is created or exists, but RDBMS tells about the relation between the table and other tables.
• RDBS supports a tabular structure for data and relationship between them in the system whereas DBMS supports only the tabular structure.
• DBMS provide uniform methods for application that has to be independently accessed, but RDBMS doesn’t provide methods like DBMS but provide relationship which link one entity with another.

55. What Do You Understand By Cardinality And Why It Is Used?

Cardinality is important and used to arrange the data inside the database. It is related to the design part and need to be properly used in database. It is used in E-R diagrams and used to show the relationship between entities/tables. It has many forms like the basic is one to one, which associate one entity with another.

Second is one to many:
which relates one entity with many entities in a table.
Third is many to many M:
N that allows many entities to be related to many more.
Last is many to one:
that allows the many entities to be associated with one entity.

56. What Is Relationship?

It is an association among two or more entities.

1. Relationship Set
   – The collection (or set) of similar relationships.
2. Relationship Type
   – Relationship type defines a set of associations or a relationship set among a given set of entity types.
3. Degree of Relationship Type
   – It is the number of entity type participating.

57. What Is The Purpose Of Acid Properties?

ACID stands for Atomicity, Consistency, Isolation and durability and it plays an important role in the database. These properties allow the database to be more convenient to access and use. This allows data to be shared more safely in between the tables. If these properties are not being implemented then the data will become inconsistent and inaccurate. It helps in maintaining the accuracy of the data in the database.

58. What Do You Understand By Data Independence?

Data independence te
lls about the independence of the data inside the application. It usually deals with the storage structure and represents the ability to modify the schema definition. It doesn’t affect the schema definition which is being written on the higher level. There are two types of data independence:

1. Physical data independence:
   it allow the modification to be done in physical level and doesn’t affect the logical level.
2. Logical data independence:
   it allow the modification to be done at logical level and affects the view level.

NOTE: Logical Data Independence is more difficult to achieve.

59. What Is Vdl?

VDL (View Definition Language): It specifies user views and their mappings to the conceptual schema.

60. What Is Ddl?

Data Definition Language : A data base schema is specifies by a set of definitions expressed by a special language called DDL.