Are you gearing up for your next SQL interview? As an SQL developer, mastering complex SQL queries is crucial to cracking that coveted job opportunity. In this competitive landscape, knowing the types of complex SQL interview questions you can expect can make all the difference. This comprehensive guide offers sample complex SQL interview questions to help you assess and direct your SQL interview preparation.
Why Complex SQL Interview Questions Matter
SQL, standing for Structured Query Language, is one of the most popular languages used by professional developers. According to leading statistics, after JavaScript and Python, SQL is employed by around 51.52% of developers. For an SQL developer hoping to bag their dream job, demonstrating proficiency in handling complex SQL queries is a must.
Interviewers often use complex SQL interview questions to evaluate a candidate’s ability to navigate through intricate database problems, think critically, and devise efficient solutions. These questions test not only your technical knowledge but also your problem-solving skills, attention to detail, and ability to communicate complex ideas clearly.
Complex SQL Interview Questions and Answers
To help you kickstart your preparation, here are some sample complex SQL interview questions and answers:
1. Write a query to get the last record from a table.
SELECT * FROM Student WHERE RowID = (SELECT MAX(RowID) FROM Student);2. Write a query to get the first record from a table.
There are two ways to fetch the first record:
-- Method 1SELECT * FROM Student WHERE RowID = (SELECT MIN(RowID) FROM Student);-- Method 2SELECT * FROM Student WHERE ROWNUM = 1;3. Write a query to display the first ten records from a table.
SELECT * FROM Student WHERE ROWNUM <= 10;4. Create a table with the same structure and data as the Student table.
CREATE TABLE Student2 AS SELECT * FROM Student;5. Show only common records between two tables.
SELECT * FROM StudentINTERSECTSELECT * FROM StudentA;Complex SQL Interview Questions for Practice
Now, let’s dive into some frequently asked complex SQL interview questions to gauge your interview preparation:
Complex PL/SQL Server Interview Questions
These complex PL/SQL server questions regularly feature at tech interviews for SQL developers:
- Define and describe the usage of a linked server.
- Name and explain the different types of Joins.
- Explain the different types of authentication modes.
- Which stored procedure would you run when adding a linked server?
- Where do you think the user names and passwords will be stored in the SQL server?
- How would you add email validation using only one query?
Complex SQL Queries Interview Questions
Interview questions related to complex SQL queries are quite common at interviews for developers. These involve questions like “what SQL query would you use to”:
- Fetch the number of weekends in the current month
- Get the last 5 records from the Student table
- Get the common records present in two different tables with no joining conditions
- Display records 5 to 9 from the Employee table
- Display the last record of a table
- Display the third-last record of a table
- Convert seconds into time format
- Remove duplicate rows from a table
- Find the number of duplicate rows
- Find the fourth-highest score in the Students table using a self-join
- Show the maximum and minimum salary together from the Employees table
- Display date in a DD-MM-YYYY format
- Create an Employee_C table, which is an exact replica of the Employee table
- Drop all user tables from Oracle
- Calculate the number of rows in a table without using COUNT
- Find repeated characters from your name
- Display department and month-wise maximum salary
- Find the second-highest salary in the Employee table
- Select all records from the Student table where the names are either Anu or Dan
- Select all records from the Student table where the name is not Anu and Dan
- Get the Nth record from the Student table
- Get the 3 highest salary records from the Student table
- Show odd rows in the Student table
- Show even rows in the Student table
- Get the DDL (Data Definition Language) of a table
- Get all records from Employees who have joined in the year 2020
- Find the maximum salary of each department
- Find all Employees with their managers
- Display the names of employees who joined in 2020 and have a salary greater than 50,000
- Get the first 5 records from the Student table
- Get information of Employees where the Employee is not assigned to any department
- Show numbers from 1 to 100
- Find duplicate rows in a table
- Get the previous month’s last day
- Display a string vertically
- The marks column in the Student table contains comma-separated values. How would you calculate the number of those comma-separated values?
- Get the 3rd highest salary using the RANK function
- Create a table with its structure the same as the Student table
- Display the first 25% of records from the Student table
- Display the last 25% of records from the Student table
- Create a table with the same structure and data as the Student table
- Get only the common records between two tables
- Get unique records from the table without using the DISTINCT keyword
- Find the admission date of the Student in YYYY-DAY-Date format
- Convert the system time into seconds
- Display the monthly salary of an Employee given the annual salary
- Get the first record from the Student table
- Get the last record from the Student table
Expert Insights
Manish Devgan, CPO of the real-time data platform, Hazelcast, says, “Markets such as retail, e-commerce, and energy are seeing growing interest in applications where data has to be processed and analyzed in real-time. The use of SQL within streaming systems opens up a new chapter in the story of SQL within the data domain.”
Frequently Asked Questions
1. What is a complex SQL query?
Complex SQL queries are parameter queries that go beyond the standard SQL usage of SELECT and WHERE and use two or more parameters. They also often heavily use AND and OR clauses. Complex queries are helpful because we can make more precise and accurate database searches with them.
2. How many types of SQL are there?
There are five types of SQL commands based on the functionalities performed by them: DDL (Data Definition Language), DQL (Data Query Language), DCL (Data Control Language), DML (Data Manipulation Language), and TCL (Transaction Control Language).
3. Give a comparison between PostgreSQL and MongoDB.
PostgreSQL is a SQL database that uses tables with organized rows and columns for storing data. It is compatible with notions like JOINS and referential integrity entity-relationship. PostgreSQL uses SQL as the query language. On the other hand, MongoDB is a NoSQL database. It can store raw data because a schema is not necessary. Data is kept in BSON documents, and the user can modify the document’s structure. The query language used by MongoDB is JavaScript.
4. What is the difference between simple and complex views in SQL?
Simple views in SQL can contain only one base table. On the other hand, complex views in SQL have more than one base table. Complex views can also have a GROUP BY clause, join conditions, and ORDER BY clause.
5. What is a unique key in SQL?
The collection of data or columns in a table that allows us to recognize records distinctively is known as a unique key in SQL. The unique key ensures that the columns in the database are all unique. It is equivalent to the primary key; however, it may accept a null value compared to it.
Conclusion
Mastering complex SQL queries is essential for anyone aspiring to land their dream job as an SQL developer. By practicing the sample complex SQL interview questions provided in this guide, you can assess your preparation level and identify areas that require further attention.
Remember, cracking a technical interview is not just about memorizing answers; it’s about developing a deep understanding of the concepts and being able to apply them effectively. With dedication and persistent practice, you can become proficient in handling complex SQL queries and increase your chances of acing your next SQL interview.
