Common SQL Problems
Did you know that the average salary of an SQL server developer ranges around 2-9 LPA?
With only two years of experience in this field you can become one of the top SQL developers and start earning a minimum of 4.5 L a year!
SQL is more commonly known as Structured Query Language. It is a different sort of programming language that has been designed to facilitate the performance of the preexisting programming languages such as Java and Python.
So, what is the task of an SQL developer? Well, an SQL developer is basically required to create powerful editors by working with developers of the other programming languages such as Python, Java and C++
This is why along with the other concepts of programming, SQL problems and solutions are also a major part of technical interviews especially for the online test and the coding rounds.
If you are interested in finding out more about the SQL problems, check out some of the most common SQL problems mentioned in the blog.
What is SQL?
Commonly referred to as a Structured Query Language, SQL, is one of the many concepts of Data Structure that allows you to manage and manipulate databases.
Did you know?
Back in 1987, SQL was announced as the standard for the International Organization for Standardization.
Check out the following functions performed by SQL for data assessment and manipulation:
- SQL allows you to execute queries for the databases
- You can also retrieve data from specific databases using SQL
- SQL can also help in inserting records within a database
- You can also delete records using SQL in a database
- SQL also allows you to create new database
- Finally, you can also manage the permissions for databases on tables, views and procedures using SQL
Now, SQL might certainly be a standard language but it does contain different versions. This question is often raised in coding interviews.
In order to tackle SQL problems and solutions, it is important to learn the major commands of the language such as WHERE, INSERT, DELETE, UPDATE and SELECT.
If you’re new to programming and are trying to learn SQL for your coding interviews, we would certainly recommend you to check the next section for some of the most commonly asked SQL problems.
How to solve common SQL problems?
The coding online tests for the technical interviews often ask SQL based problems in the form of MCQs.
That certainly doesn’t mean that you would not have to perform all the algorithms and functions for solving the problems.
Check out some of our top picks for the coding online test problems based on SQL.
- Combining two tables
This is a data allocation based problem. Have a look at the problem statement.
You are given two different tables, one named person and another called address. Your task is to compile an SQL query report for the first and last name, the city and the state of each of the people within the Person Table.
- We can use the JOINS approach for solving the problem statement. There are different forms of joins out of which choosing one is the challenge
- Since we are only provided the names of the columns within the table and the rows remain empty, we need to implement the left join in this case
- Hence, simply perform a left join using which you can draw a MySQL query that will further start matching the elements
- Finding out customers who never placed the order
In this problem statement, you are required to figure out the customers who never placed an order using an SQL query.
You are given two tables namely, Customers and Orders. Your task is to figure out the customers who have never placed an order using the SQL query and form a report based on the information collected.
The best approach to attempt this problem would be using the WHERE NOT EXISTS function.
- Firstly, we need to form a subquery where we will be selecting the customer IDs from the Orders column and matching it with the Orders table
- The main task is to identify the customer IDs that are missing from the Orders table and simply unselect these IDs in the newly formed Sub-query
- You can perform this task by using the NOT EXISTS function
Finding the second highest salary
The task of this problem statement is pretty simple. You would have to find the second highest salary from a given data.
You are provided an Employee table off which your task is to find the second highest salary. In case there are no second highest salaries, print the output as NULL.
This problem statement can be easily solved by using the Limit and Offset functions.
- We will start by selecting all the salaries from the given table and arrange them in a descending order
- Then we will move forward and limit the given salaries by 1. This way we will be able to select the second highest salary and not the highest.
Finding Duplicate Emails
Here in this problem we are referring to the same emails that we have received more than once.
Given a Person Table, find the list of duplicate emails.
There are two sets of keywords that will help in identifying the duplicate set of emails
- Before approaching this problem, we need to understand that duplicate emails are the ones that have been received more than once
- Start by selecting the data in the Person’s column and use the Group by and Having keywords to sort the list of emails that are duplicates in the table
SQL is a programming language that is most commonly used by the SDE or SQL developers.
We would like to share that learning SQL is much simpler than learning the other programming languages since it comes in a structured format.
For any queries that you have regarding solving the SQL coding online test problems, refer to our website for some of the best resources to help you in solving SQL problems.
Learn more about SQL and its core properties by checking out our website.