Interview Questions and Answers for 'Database' | Search Interview Question

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Q101. How would you securely migrate a database to RDS?

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Q102. Difference between multi AZ RDS and Read replicas ?

Amazon Web Services (AWS)

Ans. Multi AZ RDS is for disaster recovery and failover whereas Read replicas are for scaling.

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Q103. What is the limit of read replicas per database ?

Amazon Web Services (AWS)

Ans. 5

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Q104. What is the ideal use case for DynamoDB ?

Amazon Web Services (AWS)

Ans. Fast reads
Much more reads than writes

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Q105. What are the factors on which RedShift is priced on ?

Amazon Web Services (AWS)

Ans. Compute Node Hours
Backup
Data Transfer

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Q106. create an SQL query across multiple tables involving outer joins

Database

Ans. Select * from table1 t1Left outer join table2 t2 on t1.tid = t2.id

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Q107. Difference between composite , primary and unique key ?

Database

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Q108. Can we load Yaml files into AWS DynamoDB ?

Amazon Web Services (AWS)

Ans. No

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Q109. What is the minimum number of tables required to perform a SQL join?

Database

Ans. 1 , We can do self join

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Q110. Sort an Employee Object based on Name or Age

Database

Ans. Use Comparable or Comparator interface

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Q111. Create DB schema for Employee, Department.

Database

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Q112. Differences between MongoDB and mysql.

Database

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Q113. Write SQL query to join 2 tables ?

SQL

Ans. Select * from table1 join Select * from table2

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Q114. SQL Questions.

Database

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Q115. Explain Working of joins in sql.

Database

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Q116. How can we increase the speed of SQL queries ?

Database

Ans. Using -
1. Prepared Statements
2. Using Indices
3. Using whereby clause only on indexed columns

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Q117. What is a composite primary key and foreign key ?

Database

Ans. The combination of values from multiple columns in the composite primary key must be unique for each row in the table.
A foreign key, on the other hand, is a field or set of fields in one table that refers to the primary key in another table. It establishes a relationship between two tables based on the values of the foreign key and the primary key.

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Q118. differences between drop , delete and truncate

Database

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Q119. How would you design the database schema for an event?

Database

Ans. Broad question, but if the company need velocity, think about use a NO SQL instead of regular SQL databases.

Also prefers materialized views instead of joins to fetch data quickly.

Regarding the database design, there are very good design tools for professional database (to develop proper indexes and good database design) one of the best is QuickDBD

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Q120. What is the main difference between unique key and primary key ?

Database

Ans. Primary key will not accept NULL values whereas Unique key can accept one NULL value.

A table can have only primary key whereas there can be multiple unique key on a table.

A Clustered index automatically created when a primary key is defined whereas Unique key generates the non-clustered index.

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Q121. What is Dirty Read in Database Transactions ?

Database

a. Data Read by Transaction 2 which hasn't yet updated by Transaction 1

b. Data Read by Transaction 2 which has been updated and commited by Transaction 1

c. Data Read by Transaction 2 which has been updated but not commited by Transaction 1

d. Inability of Transaction 2 to read Data when Transaction 1 is updating.

Ans.c. Data Read by Transaction 2 which has been updated but not commited by Transaction 1

Q122. In majority of the cases, the following join will give maximum number of results ? Reference

Database

a. Inner Join

b. Outer Join

c. Left Join

d. Right Join

Ans.b. Outer Join

Q123. Which if the following is true for SQL Joins ? Reference

Database

a. Left Join and Right Join gives equal number of Results

b. Outer Join and Inner Join gives equal number of Results

c. Inner Join gives maximum number of results records

d. Inner Join gives minimum number of result records

Ans.d. Inner Join gives minimum number of result records

Q124. Which of the following is not true for Prepared Statements ?

Database

a. Prepared Statements provides better performance

b. Prepared Statements prevent SQL Injection attacks

c. Prepared Statements provide ORM capabilities

d. Prepared Statement provides DB side caching

Ans.c. Prepared Statements provide ORM capabilities

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