DBMS Interview Questions

DBMS Interview Questions

Are you looking to join industry as a DBMS developer? Have you prepared yourself to face DBMS interview questions? If not, then dig into some technical insights for DBMS. Database management has become popular more than ever. A set of logically arranged data for a specific purpose is commonly known as Database. A collection of programs, which can be used to create and maintain a database is known as Database Management System or DBMS. It is basically a systematic way of executing a command with data.

If one is through with the basics, half the battle is won. The more the knowledge on the subject, the easier will it be to crack the DBMS interview questions. There is a vast list of the questionnaire available on Google to help you gain confidence before facing the interview panel.

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DBMS Interview Questions

Data independence reflects data transparency and specifies that the application is independent of storage structure and access strategy of data. It modifies the schema definition in one level without changing the schema level in the next level. Physical data independence and logical data independence are two types of data independence.
It is imperative that transactions are kept as short as possible. It should be short in order to reduce contention for resources. The following are few guidelines for coding transactions efficiently –
  • It doesn’t require input from users during transactions.
  • Transactions must not be opened while browsing through data.
  • Make use of lower transaction levels.
  • While transacting, least information of data must be accessed.
There are two types of Cursor in MSSQL-
  • Implicit cursor– Implicit cursors are automatically created whenever an SQL statement is executed and this happens without the user’s notice.
  • Explicit cursor– Explicit cursors are created with the awareness of users. It handles the SQP/PL query in one row and exercises more control over the context area.
There are four types of Database language, i.e. DDL, DML, DCL, and TCL which are used for reading, updating data in Database.
  • DDL– Data Definition Language which includes CREATE, ALTER, DROP.
  • DML– Data Manipulation Language which includes SELECT, UPDATE, INSERT, etc.
  • DCL– Data Control Language which consists of GRANT and REVOKE.
  • TCL– Transaction Control Language such as COMMIT and ROLLBACK.

Nested loop- A nested loop is a loop within a loop. It is an inner loop within an outer body that allows fewer entries. Individual entries in nested loop is processed individually in the inner loop. Example-


.Select col.*, col2.* from coll, col2 where coll.coll=col2.col2;

The nested way works in following format-

For i in (select*from coll) loop

For j in (select*from col2 where col2 = i.coll) loop

Results are displayed

End of the loop;

End of the loop;

For nested loop, first outer (driving) table is identified. Then inner tavle is assigned to the outer table and every row in inner column is accessible from every row of outer table. Nested loop is executed from hash join, inner loop and then outer loop.

Hash join- it is divided into-

  • Build- this hash table has in-memory which is present on the smaller table.
  • Probe – it is the hash value present in each second row element.
  • Sort merge element- it joins two independent sources of data.

It is considered a better option as compared with nested loop when data volume is big. The full operation of hash join can be classified as-

Sort join operation-

Get first row R1 from input1

Get first row R2 from input2

Merge join operation- 'while' command is not used at loop's end.

If R1 joins with R2

Next row is got R2 from the input2

Return  (R1,R2)

else if R1 ,style="". Next row is got from R1 from

input1

else

next row is got from R2 from input 2

end of the loop.
Database language is used to create and store data in computer system. DBMS itself is one of the features of database language which is a software application for management of data. Database language also facilitates modification and alteration of query results by averaging, counting, summing, etc. Database language enables user’s interaction with other applications.
Database partitioning is the process of splitting large tables into smaller database entities. Following are the benefits of partitioning-
  • When rows are in one partition, query performance in such situations is improved.
  • It also helps to access large parts of single partition.
  • Data which are rarely used can be stored in slower and cheaper storage medium.
File processing system is inconsistent and insecure. There are also chances of data redundancy and duplication. Sometimes, it gets difficult to access data and concurrent access is also not supported. There is scope of data isolation and integrity.
DDL commands are used to modify and edit the structure of a database system. Some of the important commands are-
  1. CREATE table command- It defines each column of the table in a unique and distinct manner like name, data type, size, etc.

    Syntax: CREATE TABLE [column name] ([column definitions]) [table parameters]

  2. ALTER table command- ALTER is used to make changes and edit the existing table of database. Syntax: ALTER objecttype objectname parameters.

  3. DROP table command – DROP is used for destroying a table and all the recorded data in it. It destroys an existing database.  Syntax: DROP objecttype objectname parameters.

Join depicts the relationship between two or more tables. It combines row of different tables and enables you to select data with reference to data of some other table. There are several joins in database like CROSS JOINs, NATURAL JOINs, EQUI-JOIN, etc. Two most important joins are –

  • INNER JOIN – this join returns values that have matching record in both the tables. In this, blank rows are combined in middle.
  • OUTER JOIN– it returns all the records of left table. It also returns the values that match with the right table. Blank rows are put in specified side by joining tables in other side.
There are certain restrictions that are applied while creating views in database-
  • Only current database can have views. No other database is allowed to have views other than the current database.
  • You cannot make any changes in the computed values of any view.
  • You cannot apply full text index definitions.
  • Temporary views cannot be created and temporary tables cannot have views.
  • It is not associated with any default definitions.
  • There are integrity constants that define the working of commands such as insert and delete.
  • Triggers such as INSTEAD of is associated with views.
DBMS (Database Management System) is a computer software application that allows users and other applications to view, monitor and analyze data. It is an application to handle data on various subjects.
There are three main transaction phases in database which includes analysis phase, redo phase and undo phase.