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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 around 51.52% of developers.
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 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 for practicing 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 min:
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.
select * from Student where Rownum <= 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.
Select * from Student;
Intersect
Select * from StudentA;
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
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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.
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