Over the years, database fields have advanced, and database management systems are widely in use by organizations. With the rise of the IT field, an enormous amount of data is generated every day. To quickly and effectively access and share big data for analysis and interpretation, a DBMS is essential for organizations.
This article covers all the most important and commonly asked "Database" interview questions and answers, which will help beginners and experienced to crack any interview. Similar to any other interview, the interviewer is likely to examine both your technical and theoretical talents listed on your resume.
-You must have a thorough knowledge of various technology listed in your resume.
-Stay up to date on the latest trends in the field, and a strong command of the fundamentals is required.
-Be prepared to demonstrate your technical skills to the interviewer.
-At last, prepare with the most asked Database interview questions listed below!
Q1.What is a ‘Database’?
A database is a collection of structured and stored data that can be used to accomplish a specific task. Example: A library is a database of Books, where books are placed in different sections as per the subjects.
Q2.What do you understand by ‘DBMS’?
DBMS stands for Database Management System. It is a collection of application programs that allow the user to organize, restore, and retrieve information about data efficiently and as effectively as possible.
Q3.What is RDBMS?
RDBMS stands for "Relational Database Management System." It is based on a relational model of data that is stored in databases in separate tables, and they are related by the use of a common column.
Data can be accessed easily from the relational database using Structured Query Language (SQL).
Q4.What do you understand by Data Redundancy?
The Duplication of data in the database is known as data redundancy. Because of data redundancy, duplicated data exists in multiple locations, wasting storage space and compromising data integrity.
Q5.What is a "record" in a database?
A ‘record’ is the collection of values or fields of a specific entity.
Q6.What is a ‘field’ in a database?
A ‘field’ is an area within a record reserved for a specific piece of data. Fields are organized into records, which contain all the information within the table relevant to a specific entity.
Q7.What are database languages? What are the types?
To create or write database management systems, database languages are used. They are mainly of three types:
-Data definition language
-Data manipulation language
Q8.What is a ‘unique key’?
The unique key is the same as the primary key, with the difference being the existence of null. The unique key field allows one value as a NULL value.
Q9.What is a ‘composite key’?
A ‘composite key’ is a combination of two or more columns in a table that can be used to uniquely identify each row in the table.
Q10.What is a ‘foreign key’?
A ‘foreign key’ is a field (or collection of fields) in one table that uniquely identifies a row in another table or the same table.
Q11.What is a ‘cursor’?
A cursor is a database object that helps in manipulating data row by row, representing a result set.
Q12.What are the different types of cursors?
The different types of cursors are:
Implicit cursor: Declared automatically as soon as the execution of SQL takes place without the awareness of the user.
Explicit cursor: Defined by PL/ SQL this handles queries in more than one row.
Q13.What are Joins? Mention the various types of joins.
Joins exhibit two or more tables and are primarily of four types:
-Outer Join is subdivided into two types: right outer join and left outer join.
Q14.What do you understand by Data Independence? What are its types?
Data independence refers to the capability to change the schema definition at one level in such a way that it does not affect the schema definition at the next higher level.
There are two types of data independence:
-Physical Data Independence: It changes the schema at the physical level without affecting the schema at the conceptual level.
-Logical Data Independence: It changes the schema at the conceptual level without affecting or causing changes in the schema at the view level.
Q15.What is SQL?
Structured Query Language (SQL) being ANSI standard language updates database and commands for accessing.
Q16.Differentiate between ‘DELETE’, ‘TRUNCATE’ and ‘DROP’ commands.
Q17.What is Database partitioning?
Data partitioning is a partition of the logical database into independent, complete units for improving its management, availability, and performance.
Q18.Explain the importance of partitioning.
The importance of database partitioning is:
- To significantly improve query performance in situations where the majority of heavily accessed rows are in a single partition
- Accessing large parts of a single partition
- Slower and cheaper storage media can be used for data that is rarely used.
Q19.Explain the Database transaction.
A database transaction (DB transaction) is a unit of work performed within a database management system. It can be either completed or uncompleted as a unit.
The system will reflect successful completion after the transaction is completed; if the transaction fails, no change will be reflected. Database transaction processing helps maintain the integrity of the database.
Q20.What are the different types of manipulation possible in manipulating a database?
The different types of manipulation possible in manipulating a database are:
-Performing Calculations on data
-Editing the database
Q21.Explain Database Index and Index hunting.
A database index is a data structure that advances the speed of data retrieval operations on a database.
The procedure of increasing the collection of indexes is known as "index hunting." It improves the speed and query performance of the database. It can be done by various methods, such as query optimization and query distribution.
Q22.What are the different types of indexes?
There are three types of indexes:
-Unique Index: This indexing does not allow the field to have duplicate values if the column is uniquely indexed. A unique index can be applied automatically when the primary key is defined.
-Clustered Index: This type of index reverses the physical order of the table and searches based on the key values. Each table can have only one clustered index.
-NonClustered Index: NonClustered Index does not alter the physical order of the table and maintains the logical order of data. Each table can have 999 nonclustered indexes.
Q23.Explain the difference between intension and extension in a database.
Following is the major difference between intension and extension in a database:
Intension: Intension or popularly known as database schema, is used to define the description of the database. It is specified during the design of the database and mostly remains unchanged.
Extension: Extension, on the other hand, is the measure of the number of tuples present in the database at any given point in time. The extension of a database is also referred to as the snapshot of the database, and its value keeps changing as and when the tuples are created, updated, or destroyed in the database.
Q24.What are the differences between views and tables?
Here is the difference between the views and tables listed below:
Q25.What is a temporary table? Write a query to create a temporary table.
A temporary table helps us store and process intermediate results. Temporary tables are created and can be automatically deleted when they are no longer needed. They are very beneficial in places where temporary data needs to be stored.
Q26.What do you mean by SQL injection?
SQL injection is a technique used by black-hat hackers to steal data from databases or tables.
Q27.How can you add several rows in Structured Query Language?
To add several rows in a structured query language, the following syntax can be used:
Add the keywords ‘INSERT INTO’ and enter the table’s name to add values. Then move to column lists and add values for them. Then type the keyword ’VALUE’ and provide the list of values.
Q28.Explain about trigger in SQL
A trigger is a stored procedure that automatically runs when an event occurs in the database server. The automatic response to the operations of DML can be inserting, deleting, or updating a table or view.
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This article covers database interview questions for beginners and experienced candidates. If you are planning to appear in an upcoming database interview, then this set of questions will boost your preparation.
In addition to technical abilities, database professionals need to have strong problem-solving abilities, organizational skills, attention to detail, and a high degree of accuracy.
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