Best SQL Interview Questions in 2021
RDBMS is A database that is used by most developers, therefore SQL skills are very important in most job roles. In this article, We will introduce you to the most recent and frequently asked questions on SQL.
After going through this article you will get the proper concepts related to SQL, Oracle, MSSQL Server, and MySQL database.
Without any further ado let’s get straight to The top SQL interview questions which will help you to boost your interview preparation.
Top SQL interview questions in 2021
1 ) What is SQL? What are the various subsets of SQL?
SQL is a standard language that stands for a structured query language, that controls the core of relational databases which is used for accessing and managing databases.
The various subjects of SQL are:
- Data definition language(DDL)- It provides the user to perform various actions and operations on a database, for example, create, alter and delete objects.
- Data manipulation language(DML)- It allows the user to access and manipulate data which helps to insert, update, delete hundred Drive data from the database.
- Data control language- it gives access to control the database. Example grant and revoke access permissions.
2 ) What are joints in SQL?
Joins are used to merge rows and two or more tables and retrieve data from there. Four types of joints are there, as you can refer to below:
- Inner join- It is mainly used to return all the rows and multiple tables when the join condition is satisfied.
- Left join- It is used to return all the rows from the left table, only the matching rows from the right table where the join condition is satisfied.
- Right, join- It is used to return all the rows from the right of the table and matching rows from the left table when the join condition is satisfied.
- Full join- It is used to return all the records from any part of the tables.
3 ) What is the primary key?
The primary key in SQL is a collection of columns or a set of columns that uniquely identifies each room in the table and Null values are not allowed. Example: In salaried men, emp_ID is a primary key.
4 ) What is the Unique key?
It uniquely identifies a single row in the table and allows multiple values per table, Nall values are allowed in the unique key.
5 ) What do you mean by data integrity?
It is defined as the accuracy and consistency of data stored in a database. Data integrity defines how to integrate constraints and enforce business rules on the data into an application or a database.
6 ) What do you understand about Denormalization?
It is a technique that is used to access data from higher to lower forms of the database. It manages the database System to increase the performance and entire functionality as it introduces redundancy into the table.
7 ) What is a subquery in SQL? What different types of subqueries?
It is a type of query which is defined to retrieve data or information back from the database. Saab queries or executes first and then the result is passed on Main greedy for further execution.
The nested subquery Can be formed by selecting the update option. There are two types of subquery mentioned below:
- Correlated Subquery: These queries select the data from the order query and these are not considered as independent queries and refer to the column in a table.
- Noncorrelated subquery: This query is an independent query in which the output of this is substituted in the Main query.
8 ) Mention the ways to get the count of records for a table.
To count the number of records in a table, commands are mentioned below:
SELECT * FROM t1 SELECT COUNT (* ) FROM t1 SELECT rows FROM sysindexes WHERE id = OBJECT_ID(t1) AND indid < 2
9 ) Why are SQL functions used?
For various purposes SQL functions are used some of them are mentioned below:
- To do some calculations on the data.
- To change or modify individual information.
- To manipulate the output.
- To reset dates and numbers.
- To convert data types.
10 ) How can we fetch alternate records from a table?
One can fetch internet records I both Auden even do numbers by using the following command:
Select StudentID from (Select rowno, student id from student ) where mod(rowno,2) = 0
For Displaying odd numbers:
Select Student ID from (Select rowno, studentID from student ) where mod(rowno,2) = 1
11 ) What is the major difference between SQL and PL/SQL?
SQL is a query language that permits the user to issue a single query or execute/insert/Updates/delete whereas PL/SQL is a procedural language that allows the user to write a full program to execute multiple operations such as selects/insureds/Updates/delete.
12) What is the stored procedure? List some advantages of stored procedure.
A stored procedure is a function that consists of SQL statements to access the database system. SQL statements are consolidated into a stored procedure and help the user to execute whenever and wherever required which saves time and avoids rewriting of code again and again.
Advantages are as follows: It can be used as modular programming that allows the user to create the SQL statement ones and store it several times for further execution whenever it is required. It reduces the traffic and provides better security to the stored data.
These are some of the basics SQL interview questions examples, if you want to get trained from professionals on SQL stay connected to our website. I hope these chains of questions will somehow help to ace your job interview.
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All the best for your interview!