Are you preparing for a database management system interview session? If yes, then you have landed on the right page. In this blog, we will discuss the most common DBMS interview questions and answers.
Data is everywhere. It is very crucial to examine and produce meaningful outcomes from this data. There is no doubt that the demand for a database administrators is increasing day by day. The world’s most prominent organizations are looking for a database administrator.
If you are thinking of making a profession in the database sector, you should go through these DBMS interview questions and answers. If you want to know more about database management, check out our website. We provide several different technology-related courses.
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DBMS Interview Questions and Answers
The below-mentioned DBMS interview questions will assist you in clearing your concepts related to database management. Here, we will discuss the top 10 questions about database management, SQL, and their answers.
Question 1: Explain DBMS.
DBMS stands for database management systems. It is a collection of technical schemas that build and sustain a database. The database management system is software that provides a systematic method to interact with applications and databases to examine and produce the required outcome of the data. The database management system offers several operations. These include data insertion, data deletion, database creation, modification, and many more.
The top features of DBMS include the following-
- Removes redundancy
- Large Database Maintenance
- It provides high security
- Saves storage
- The SQL language is used to insert, retrieve or remove any type of data item.
- Data integrity
- Supports multiple views of data
- Allows entities and relations among them to form tables.
- Follows ACID (Atomicity, Consistency, Isolation, Durability.) concept
- Supports multi-user environment
Advantages of using DBMS-
- Data consistency
- Data Integrity
- Data backups
- Applications customisation
- Data Management
- Data durability
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The top 10 DBMS interview questions would be incomplete without making a mention of the basic DBMS question. Make sure not to neglect the simple possibilities and prepare well for them. Moreover, do not suffice your answers until the definition; mention advantages and features to add weight to your answer.
Question 2: What Are the Advantages of a Database Management System?
The significant benefits of the database management system are listed below:
- Consistency: Data is duplicated in the traditional file system. Hence, any modifications made in one part may reflect on all other parts. This further leads to inconsistent information. We need to eliminate duplicate data to remove inconsistent information throughout the system. This is possible with a DBMS.
- Elimination of Data Redundancy: The major reason DBMS is favored over the traditional file system is that it controls data redundancy. Each user handles their file in the conventional file systems. This further leads to redundancy of the same information in several distinct files, errors, wastage of resources, and storage space.
- Better Integrity: There is a lack of integrity in traditional file systems. In the DBMS approach, it is crucial to impose integrity restrictions. The database approach is much better in terms of integrity than the conventional file system because it is centralized. In the database management system, data can be utilized by several users at a time.
- Requirements Can be Examined: With the implementation of a centralized data approach, it is much easier to analyze organizations’ needs. The primary responsibility of the database administrator is to organize a well-defined database for the organization.
- Better Security: The traditional file system develops applications temporarily. The centralized approach of the database system provides various security constraints, which further improve the overall system’s security.
- Data backups: DBMS technology allows the data to be backed up efficiently. The data backup can happen from a single location very simply.
- Applications customisation: The applications can be customised according to the customer’s needs without tailoring the entire database.
- Simple data management: It provides robust tools for users to enter, delete, change or export corporate data.
- Data durability: DBMS ensures data durability. In the mishaps such as power outages or any other disaster, the data in the system remains unaffected.
- Make sure to elaborate with at least one sentence while answering the DBMS interview questions like advantages, features, etc.
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Question 3: What Is “Redo” In a Database?
“REDO” in the database is used for rollback commands. When a database transaction takes place, it goes to the database buffer cache. Then, the data is coded to “REDO” logs from the “REDO” buffer. The data recovery operations need these logs for future use. The recovery of information is not possible without these logs. The rollback command clears the undo data.
The Redo entries record the data, which the users can utilise to reconstruct all changes made to the database. The redo log also protects the rollback data.
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Question 4: Explain the Difference between “GROUP BY” and “ORDER BY”.
|S.No.||GROUP BY||ORDER BY|
|1.||The GROUP BY command is used to combined data||The ORDER BY operation is used for sorting data|
|2.||It is utilized to form summaries in the result section||It is utilized for sorting results by a list of expressions|
|3.||The SQL clause specifying with the SELECT statement to retrieve data, gets grouped according to the one or more column.||The SQL clause specifying with the SELECT statement to return a result set, where the rows gets sorted according to a specific order.|
|4.||Helps to combine the data depending upon one or more columns.||Helps to organise the retrieved data in either ascending or descending order.|
|5.||It is used to group the rows having the same value.||Sort the results either in ascending or descending order.|
|6.||Could be allowed to CREATE VIEW statement.||Not used in the CREATE VIEW statement.|
|7.||In select statements, GROUP BY is always used before the order by keyword.||In select statements, ORDER BY is used is always used after the group by keyword.|
|8.||There is no possibility of keeping the attribute in the GROUP BY statement under the aggregate function.||Attribute can be under the aggregate function.|
There is a possibility of this dbms topics for interview being asked. Make sure to apply a structure to your answer. It will help you in answering better and staying confident during the process.
Question 5: While Creating Views, What Constraints Can You Apply?
The lists of constraints that can be applied are described below:
- The definitions of a complete text index cannot be applied.
- The views are only for the current database.
- You cannot create temporary views.
- The default definitions are not associated.
- Integrity constraints decide the functionality of delete and insert command.
- Triggers are associated with views.
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Question 6: Explain All Categories of Database Languages.
The four categories of database languages are listed as below:
- Data Manipulation Language: Data manipulation languages or DML are used to make changes in updated information. The commands for data manipulation languages include update command, select command, delete command, insert command, and many more. DML commands handle the stored information in the database. These commands are not permanent. This means rollback operation is possible in DML commands.
As the name suggests, it enables the users to access and manipulate the data that is stored in the existing schema objects. The mentioned commands deal with the user requests for all data modification types. DML command dealing with data retrieval is known as Data Query Language.
Some of the DML commands are mentioned below-
- SELECT: It cannot manipulate the data, rather only access it.
- INSERT: It is used to insert the rows into the table.
- UPDATE: Helps to update the column/ table within a table.
- DELETE: It deletes the existing records from the table.
- MERGE: Merges the data from the source table to the targeted table.
- CALL: It is used to execute the Structured Query Language (SQL) from within SQL.
- Data Definition Language: Data definition languages or DDL are used to define and update the data. The commands for data definition languages include alter, create, truncate, drop, rename, and many more. The commands of data definition languages can store shared information.
It is a set of special commands that allows the users to define and modify the structure and the metadata of the database. Its commands can alter the structure of the database. Each change that is implemented by the DDL command is auto-committed.
Some of the DDL commands are mentioned below-
- CREATE- Creates the database or its schema objects.
- DROP: Deletes the database or its schema objects.
- ALTER: Modifies the structure of the database objects.
- TRUNCATE- Removes the whole content of the table along with deallocation without affecting the structure.
- COMMENT: Adds comments about the views, tables, and columns into the data dictionary.
- RENAME: Helps in changing the name of the existing table or a database object.
- Transaction Control Language: Transaction control languages or TCL are used for handling database transactions. The commands for transaction control languages consist of rollback, commit, savepoint, and many more. Transaction languages are mainly used for handling the modifications made by data manipulation languages.
- They are the special commands that deal with transactions within a database. The transactions play an important role for the execution of different tasks within a database. Thet ara a collection of different tasks that are treated as a single execution unit by DBMS.
Some of the TCL commands are mentioned below-
- COMMIT: It is used to permanently save all the modifications that are done by the DML commands.
- ROLLBACK: It undoes the transactions that have not already been permanently saved or committed.
- SAVEPOINT: Creates a point within the groups of transactions. It does so to either save or roll back later.
- AUTOCOMMIT: Either enable/ disable the auto-commit process that commits each transaction after its execution.
- Data Control Language: Data control languages or DCL are used to take away or give database access to a user. The commands data control languages are “revoke” and “grant.” The syntax of the data control language is similar to the coding language. Data control language is related to security concerns. The GRANT DCL command provides access to the user. The REVOKE DCL command is used to withdraw the access privileges.
It acts as a set of special commands that control the user privileges in the database system.
Some of the DCL commands are mentioned below:
- GRANT: Provides user access to the database or its objects.
- REVOKE: Revokes user access to the database system.
This is one of the DBMS important interview questions; collect your thoughts before answering this question. It will help you to answer smoothly without appearing flustered.
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Question 7: What Is the Difference between Data Definition Language and Data Manipulation Language?
|S.No.||Data Definition Language||Data Manipulation Language|
|1.||DDL commands are used to define the structure of the database||DML commands handles the stored information in the database|
|2.||Data definition language is not categorized further||Data manipulation language is categorized as procedural DML and non-procedural DML|
|3.||The statements of data definition language can affect the complete table||The statements of data manipulation language can affect one or more rows|
|4.||The commands of data definition language are used to create the database structure.||The commands of data manipulation language are used to manipulate the database|
|5.||DDL commands define the table column||DML commands update the table row|
|6.||Data definition language is declarative||Data manipulation language is imperative|
|7.||DDL commands include truncate, alter, create, rename and drop, etc.||DML commands include update, delete, merge and insert, etc.|
|8.||Changes cannot be rolled back.||Changes can be rolled back.|
|9.||It does not have a where clause to filter.||It has the where clause to filter records.|
|10.||Used to create the database schema.||It is used to populate and manipulate the database.|
Question 8: Define the Nested Loop with an Example.
It is a loop over a loop. It includes some entries of the outermost loop within an internal loop. The nested loop follows three steps. First is the identification of the outermost table. Second is allocating the internal table to the outermost table. Then, for every outermost table row, retrieve the internal table rows. Let’s consider an example.
Select row4.*, row5.* from rows, row5 where rows.row 4 =row 5.row 5;
The processing of the above query will take place in the below method:
- For I loop (select *from row4)
- For J loop (select * from row5 where row5=I.row 4)
- Loop end;
- Loop end;
Features of the nested loop-
- For loop can be put inside another for a loop.
- It is a loop within a loop.
- Any number of loops can be defined inside another loop.
- The nesting level can be defined n times.
- Any type of loop can be defined inside another loop.
- A while loop can be defined inside a for loop.
The main advantage of the nested loop is that it can help in quick retrieval of the first few rows of the result set. The process can be done without having to wait for the entire result to be determined.
DBMS interview questions and answers like this should be answered keeping the holistic view in mind. Make sure to mention the features, advantages or both. It adds depth to your answer. It makes for the most important DBMS interview questions. Make sure not to miss this topic while preparing.
Question 9: Explain the 3-Tier Database Management System Architecture.
This architecture includes a layer between the server and the client. The server-end application interacts with the client-end application for further communication process in the database system. The three-tier architecture offers GUI, which further secures the database system. The three-tier architecture consists of four levels. These levels include external, conceptual, internal, and physical levels.
Advantages of 3-Tier Database Management System Architecture-
- Improves scalability: The application server can be deployed on many machines. Any tier can be scaled independently of others.
- Faster development: Each tier can be developed simultaneously by different teams.
- Enhanced reliability: Performance in one tier is less likely impact the performance of another tier.
- Easy to maintain and modify.
- Better to re-use.
- Easier modification.
This makes for top interview questions on dbms, prepare well for this question. Along with explaining the topic, make a slight mention of advantages, features or both. These types of dbms question are asked to understand the technical hold of the interviewee.
Question 10: Explain the difference between the “TRUNCATE” and the “DELETE” Command.
|S.No.||TRUNCATE Command||DELETE Command|
|1.||This command removes all the table rows||This command deletes only specific rows of the table|
|2.||This command doesn’t keep a log||This command handles a log|
|3.||Truncate cannot be a rollback||The delete can be a rollback operation|
|4.||Truncate is a fast command||Delete is a slow command|
|5.||The truncate command uses table log||Delete command uses row log
|6.||Marks the extents of a table for deallocation.||Removes one or more records from a table inside the database.|
|7.||Not possible to use where clause.||Possible to use where clause.|
|8.||Cannot use indexed views.||Can use indexed views.|
|9.||Reset the high level watermark.||Won’t reset the high level watermark.|
|10.||No triggers will get fired.||Triggers will get fired.|
DBMS basic interview questions like this can be expected during the interview. DBMS interview question like such would be asked by the interviewer would ask these type of differences to determine your clarity of thought.
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