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Complex SQL Interview Questions for Interview Preparation

by Interview Kickstart Team in Interview Questions
October 10, 2024
Learn how to ace SQL interviews

Complex SQL Interview Questions for Interview Preparation

Last updated by Swaminathan Iyer on Oct 04, 2024 at 04:15 PM | Reading time: 9 minutes

You can download a PDF version of  
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Complex SQL Interview Questions: According to the leading statistics, SQL is one of the most popular languages used by professional developers. It has been found that after JavaScript and Python, SQL is used by 51.52% of developers.

Medium SQL Usage

For an SQL developer hoping to bag their dream job, mastering complex SQL queries is a must for cracking that SQL interview. In this competitive space, the importance of knowing the kind of complex SQL interview questions for experienced professionals you can expect can’t be overstated. This article offers sample complex SQL interview questions to help you assess and direct your SQL interview preparation.

In this article, we have presented some of the complex SQL interview questions for interview preparation for experienced developers and some that you can follow to practice your answers.

Complex SQL Interview Questions and Answers for Experienced Developers

Here are some sample complex SQL interview questions and answers to help you with your complex SQL preparation:

Q1. Write a Query to Get the Last Record from a Table

To get the last record from a table, you can use the `ORDER BY` clause in combination with the `LIMIT` clause (or its equivalent in different SQL dialects). Here’s how you can do it:


For SQL databases like MySQL, PostgreSQL, and SQLite:

SELECT * 
FROM Student
ORDER BY RowID DESC
LIMIT 1;

For Oracle:

SELECT * 
FROM (            
    SELECT *           
     FROM Student      
     ORDER BY RowID DESC
)
WHERE ROWNUM = 1; 

For SQL Server:

SELECT TOP 1 * 
FROM Student 
ORDER BY RowID DESC;


These queries will fetch the last record from the `Student` table based on the `RowID` column.

Q2. Write a Query to Get the First Record from a Table?

The first record can be fetched in two ways, one similar to the last record case, but with use of min:

First way: select * from Student where RowID = select min(RowID) from Student;

The other method is by printing just one (first) row of the table:

select * from Student where Rownum = 1;

Q3. Write a Query to Display the First Ten Records from a Table.

Consider the table: 




Student ID
First Name Last Name Age Grade
1
John
Doe 20
A
2 Jane
Smith 21 B
3 Michael
Johnson
22 A
4 Emily
Davis 19 B
5 David
Wilson 23 C
6 Sarah
Brown 20 A
7 Chris
Taylor 21 B
8 Linda
More 22 A
9 James
Clark 20 B
10 Olivia
Lewis 19 A
11 Robert
Walker 22 B
12 Jessica
Hall 21 A

To list out only the top 10 rows use this code using ROWNUM: 

SELECT * FROM Student WHERE ROWNUM <= 10;

Using LIMIT:

SELECT * FROM Customers LIMIT 10;

Q4. Create a Table with the Same Structure with Data as in the Student Table.

To create a table with the same structure and data as the `Student` table, you can use the `CREATE TABLE AS SELECT` statement in SQL. Here’s how you can do it:

CREATE TABLE Student_Copy AS
SELECT *
FROM Student;

This query will create a new table called `Student_Copy` with the same structure and data as the `Student` table. If you only want to copy the structure without the data, you can add a `WHERE` clause that evaluates to false:

CREATE TABLE Student_Copy AS 
SELECT *
FROM Student
WHERE 1=0;

This will create the `Student_Copy` table with the same structure but without copying any data from the original `Student` table.

Q5. Show Only Common Records Between Two Tables.

Here let's consider 2 tables: student and student1. 

Table 1: student

Select * from student 

student 1

Table 2: student1

student 2

Select * from student1

Final Query: 

(Select * from student) Intersect (Select * from student1)

Final Output: Here in the output table we can see only the common rows from both tables being displayed. 

Final output

Complex SQL Interview Questions for Practice

Now, check out these 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:

6. Define and describe the usage of a linked server.

7. Name and explain the different types of Joins.

8. Explain the different types of authentication modes.

9. Which stored procedure would you run when adding a linked server?

10. Where do you think the user names and passwords will be stored in the SQL server?

11. 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”:

12. Fetch the number of Weekends in the current month

13. Get the last 5 Records from the Student table

14. Get the common records present in two different tables that have no joining conditions.

15. Display records 5 to 9 from the Employee table.

16. Display the last record of a table

17. Display the third-last record of a table

18. Convert seconds into time format

19. Remove duplicate rows from a table

20. Find the number of duplicate rows

21. Find the fourth-highest score in the Students table using self-join

22. Show the max and min salary together from the Employees table

23. Display date in a DD-MM-YYYY table

24. Create Employee_C table, which is the exact replica of the Employee table

25. Drop all user tables from Oracle

26. Calculate the number of rows in a table without using count

27. Find repeated characters from your name

28. Display department and month-wise maximum salary

29. Find the second-highest salary in the Employee table.

30. Select all the records from the Student table, where the names are either Anu or Dan.

31. Select all the records from the Student table where the name is not Anu and Dan.

32. Get Nth Record from the Student table.

33. Get the 3 Highest salaries records from the Student table

34. Show Odd rows in the Student table

35. Show Even rows in the Student table

36. Get the DDL of a table

37. Get all the records from Employees who have joined in the year 2020.

38. Find the maximum salary of each department.

39. Find all Employees with their managers.

40. Display the name of employees who joined in 2020 and have a salary is greater than 50000.

41. Get the first 5 Records from the Student table.

42. Get information of Employees where Employee is not assigned to any department.

43. Show 1 to 100 Numbers

44. Find duplicate rows in a table

45. Get the previous month’s last day.

46. Display a string vertically.

47. The marks column in the Student table contains comma-separated values. How would you calculate the number of those comma-separated values?

48. Get the 3rd highest salary using Rank Function.

49. Create a table with its structure the same as the structure of the Student table.

50. Display first 25% records from the Student table

51. Display last 25% records from the Student table

52. Create a table with the same structure and data as the Student table

53. Get only the common records between two tables

54. Get unique records from the table without using distinct keywords.

55. Find the admission date of the Student in YYYY-DAY-Date format.

56. Convert the System time into seconds.

57. Display monthly Salary of Employee given annual salary.

58. Get the first record from the Student table

59. Get the last record from the Student table

Ready to Nail Your Next Coding Interview?

Whether you’re a coding engineer gunning for a software developer or software engineer role, a tech lead, or you’re targeting management positions at top companies, IK offers Backend Engineering course specifically designed for your needs to help you with your technical interview preparation!

As pioneers in the field of technical interview preparation, we have trained thousands of software engineers to crack the toughest coding interviews and land jobs at their dream companies, such as Google, Facebook, Apple, Netflix, Amazon, and more!

FAQs on Complex SQL Interview Questions

Q1. 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.

Q2. How Many Types of SQL Are There?

There are five types of SQL commands on the basis of 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).

Q3. 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 is capable of storing 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.

Q4. 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.

Q5. 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.



Related reads:





Author
Swaminathan Iyer
Product @ Interview Kickstart | Ex Media.net | Business Management - XLRI Jamshedpur. Loves building things and burning pizzas!
The fast well prepared banner

Complex SQL Interview Questions: According to the leading statistics, SQL is one of the most popular languages used by professional developers. It has been found that after JavaScript and Python, SQL is used by 51.52% of developers.

Medium SQL Usage

For an SQL developer hoping to bag their dream job, mastering complex SQL queries is a must for cracking that SQL interview. In this competitive space, the importance of knowing the kind of complex SQL interview questions for experienced professionals you can expect can’t be overstated. This article offers sample complex SQL interview questions to help you assess and direct your SQL interview preparation.

In this article, we have presented some of the complex SQL interview questions for interview preparation for experienced developers and some that you can follow to practice your answers.

Complex SQL Interview Questions and Answers for Experienced Developers

Here are some sample complex SQL interview questions and answers to help you with your complex SQL preparation:

Q1. Write a Query to Get the Last Record from a Table

To get the last record from a table, you can use the `ORDER BY` clause in combination with the `LIMIT` clause (or its equivalent in different SQL dialects). Here’s how you can do it:


For SQL databases like MySQL, PostgreSQL, and SQLite:

SELECT * 
FROM Student
ORDER BY RowID DESC
LIMIT 1;

For Oracle:

SELECT * 
FROM (            
    SELECT *           
     FROM Student      
     ORDER BY RowID DESC
)
WHERE ROWNUM = 1; 

For SQL Server:

SELECT TOP 1 * 
FROM Student 
ORDER BY RowID DESC;


These queries will fetch the last record from the `Student` table based on the `RowID` column.

Q2. Write a Query to Get the First Record from a Table?

The first record can be fetched in two ways, one similar to the last record case, but with use of min:

First way: select * from Student where RowID = select min(RowID) from Student;

The other method is by printing just one (first) row of the table:

select * from Student where Rownum = 1;

Q3. Write a Query to Display the First Ten Records from a Table.

Consider the table: 




Student ID
First Name Last Name Age Grade
1
John
Doe 20
A
2 Jane
Smith 21 B
3 Michael
Johnson
22 A
4 Emily
Davis 19 B
5 David
Wilson 23 C
6 Sarah
Brown 20 A
7 Chris
Taylor 21 B
8 Linda
More 22 A
9 James
Clark 20 B
10 Olivia
Lewis 19 A
11 Robert
Walker 22 B
12 Jessica
Hall 21 A

To list out only the top 10 rows use this code using ROWNUM: 

SELECT * FROM Student WHERE ROWNUM <= 10;

Using LIMIT:

SELECT * FROM Customers LIMIT 10;

Q4. Create a Table with the Same Structure with Data as in the Student Table.

To create a table with the same structure and data as the `Student` table, you can use the `CREATE TABLE AS SELECT` statement in SQL. Here’s how you can do it:

CREATE TABLE Student_Copy AS
SELECT *
FROM Student;

This query will create a new table called `Student_Copy` with the same structure and data as the `Student` table. If you only want to copy the structure without the data, you can add a `WHERE` clause that evaluates to false:

CREATE TABLE Student_Copy AS 
SELECT *
FROM Student
WHERE 1=0;

This will create the `Student_Copy` table with the same structure but without copying any data from the original `Student` table.

Q5. Show Only Common Records Between Two Tables.

Here let's consider 2 tables: student and student1. 

Table 1: student

Select * from student 

student 1

Table 2: student1

student 2

Select * from student1

Final Query: 

(Select * from student) Intersect (Select * from student1)

Final Output: Here in the output table we can see only the common rows from both tables being displayed. 

Final output

Complex SQL Interview Questions for Practice

Now, check out these 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:

6. Define and describe the usage of a linked server.

7. Name and explain the different types of Joins.

8. Explain the different types of authentication modes.

9. Which stored procedure would you run when adding a linked server?

10. Where do you think the user names and passwords will be stored in the SQL server?

11. 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”:

12. Fetch the number of Weekends in the current month

13. Get the last 5 Records from the Student table

14. Get the common records present in two different tables that have no joining conditions.

15. Display records 5 to 9 from the Employee table.

16. Display the last record of a table

17. Display the third-last record of a table

18. Convert seconds into time format

19. Remove duplicate rows from a table

20. Find the number of duplicate rows

21. Find the fourth-highest score in the Students table using self-join

22. Show the max and min salary together from the Employees table

23. Display date in a DD-MM-YYYY table

24. Create Employee_C table, which is the exact replica of the Employee table

25. Drop all user tables from Oracle

26. Calculate the number of rows in a table without using count

27. Find repeated characters from your name

28. Display department and month-wise maximum salary

29. Find the second-highest salary in the Employee table.

30. Select all the records from the Student table, where the names are either Anu or Dan.

31. Select all the records from the Student table where the name is not Anu and Dan.

32. Get Nth Record from the Student table.

33. Get the 3 Highest salaries records from the Student table

34. Show Odd rows in the Student table

35. Show Even rows in the Student table

36. Get the DDL of a table

37. Get all the records from Employees who have joined in the year 2020.

38. Find the maximum salary of each department.

39. Find all Employees with their managers.

40. Display the name of employees who joined in 2020 and have a salary is greater than 50000.

41. Get the first 5 Records from the Student table.

42. Get information of Employees where Employee is not assigned to any department.

43. Show 1 to 100 Numbers

44. Find duplicate rows in a table

45. Get the previous month’s last day.

46. Display a string vertically.

47. The marks column in the Student table contains comma-separated values. How would you calculate the number of those comma-separated values?

48. Get the 3rd highest salary using Rank Function.

49. Create a table with its structure the same as the structure of the Student table.

50. Display first 25% records from the Student table

51. Display last 25% records from the Student table

52. Create a table with the same structure and data as the Student table

53. Get only the common records between two tables

54. Get unique records from the table without using distinct keywords.

55. Find the admission date of the Student in YYYY-DAY-Date format.

56. Convert the System time into seconds.

57. Display monthly Salary of Employee given annual salary.

58. Get the first record from the Student table

59. Get the last record from the Student table

Ready to Nail Your Next Coding Interview?

Whether you’re a coding engineer gunning for a software developer or software engineer role, a tech lead, or you’re targeting management positions at top companies, IK offers Backend Engineering course specifically designed for your needs to help you with your technical interview preparation!

As pioneers in the field of technical interview preparation, we have trained thousands of software engineers to crack the toughest coding interviews and land jobs at their dream companies, such as Google, Facebook, Apple, Netflix, Amazon, and more!

FAQs on Complex SQL Interview Questions

Q1. 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.

Q2. How Many Types of SQL Are There?

There are five types of SQL commands on the basis of 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).

Q3. 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 is capable of storing 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.

Q4. 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.

Q5. 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.



Related reads:





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Recession-proof your Career

Recession-proof your Software Engineering Career

Attend our free webinar to amp up your career and get the salary you deserve.

Ryan-image
Hosted By
Ryan Valles
Founder, Interview Kickstart
blue tick
Accelerate your Interview prep with Tier-1 tech instructors
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360° courses that have helped 14,000+ tech professionals
blue tick
57% average salary hike received by alums in 2022
blue tick
100% money-back guarantee*
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