SQL DISTINCT Clause Practice Questions with Solutions

The SQL DISTINCT keyword is used to remove duplicate values from the result set. When a table contains repeated data, DISTINCT helps return only unique records.

In real-world databases, duplicate values are common. For example:

• Multiple students may belong to the same city.
• Many employees can work in the same department.
• Several products may have the same category.

Using the DISTINCT keyword ensures that duplicate values appear only once in the query result. SQL DISTINCT Clause practice questions with solutions help to understand the concepts.

The DISTINCT keyword is commonly used in:

• Reports
• Data Analysis
• Business Intelligence Dashboards
• Customer Analytics
• Data Cleaning

What is SQL DISTINCT?

The DISTINCT keyword removes duplicate rows from the query result.

Basic Syntax

SELECT DISTINCT column_name

FROM table_name;

Multiple Columns

SELECT DISTINCT city,
                course

FROM students;

In this case, SQL returns only unique combinations of city and course.

Sample Table Used Throughout This Chapter

students

Why Use DISTINCT?

The DISTINCT keyword is useful for:

• Removing duplicate values
• Finding unique cities
• Listing unique courses
• Identifying unique departments
• Data cleaning
• Report generation
• Business analysis

1. SQL Query to Display Unique Cities

Problem Statement

Write an SQL query to display all unique cities from the students table.

SQL Solution

SELECT DISTINCT city

FROM students;

Sample Output

Explanation

Although multiple students belong to Delhi and Noida, the DISTINCT keyword returns each city only once.

Without DISTINCT, duplicate city names would also appear.

Concepts Covered

• DISTINCT
• Unique Values
• Duplicate Removal

2. SQL Query to Display Unique Courses

Problem Statement

Write an SQL query to display all unique courses offered.

SQL Solution

SELECT DISTINCT course

FROM students;

Sample Output

Explanation

Even though multiple students are enrolled in the same course, DISTINCT removes duplicate course names.

Concepts Covered

• DISTINCT
• Text Data
• Duplicate Records

3. SQL Query to Display Unique Ages

Problem Statement

Write an SQL query to display all unique student ages.

SQL Solution

SELECT DISTINCT age

FROM students;

Sample Output

Explanation

The DISTINCT keyword removes repeated age values and returns only unique ages available in the table.

Concepts Covered

• DISTINCT
• Numeric Data
• Unique Records

4. SQL Query to Display Unique Marks

Problem Statement

Write an SQL query to display all unique marks scored by students.

Sample Table

SQL Solution

SELECT DISTINCT marks

FROM students;

Sample Output

Explanation

The DISTINCT keyword removes duplicate marks (if any exist) and displays each unique mark only once.

This is useful for:

• Exam analysis
• Score distribution
• Report generation

Concepts Covered

• DISTINCT
• Numeric Data
• Duplicate Removal

5. SQL Query Using DISTINCT with Multiple Columns

Problem Statement

Write an SQL query to display all unique combinations of City and Course.

Sample Table

SQL Solution

SELECT DISTINCT city,
                course

FROM students;

Sample Output

Explanation

When multiple columns are used with DISTINCT, SQL checks the entire row combination.

Notice that:

• Delhi + Python appears only once, even though multiple students belong to this combination.
• Delhi + SQL is considered a different combination.
• Noida + Java and Noida + SQL are also different.

This feature is commonly used in reporting and analytics to identify unique combinations of data.

Concepts Covered

• DISTINCT
• Multiple Columns
• Unique Combinations
• Duplicate Row Removal

6. SQL DISTINCT with WHERE Clause

Problem Statement

Write an SQL query to display all unique cities where students scored more than 85 marks.

Sample Table

SQL Solution

SELECT DISTINCT city

FROM students

WHERE marks > 85;

Sample Output

Explanation

SQL performs the operations in this order:

1. Apply the WHERE condition (marks > 85).
2. Remove duplicate city names using DISTINCT.

Although Delhi appears more than once in the filtered data, it is displayed only once.

Concepts Covered

• DISTINCT
• WHERE Clause
• Duplicate Removal
• Filtering Records

7. SQL DISTINCT with ORDER BY Clause

Problem Statement

Write an SQL query to display all unique cities sorted alphabetically.

SQL Solution

SELECT DISTINCT city

FROM students

ORDER BY city ASC;

Sample Output

Explanation

The query first removes duplicate cities using DISTINCT.

Then, the ORDER BY clause sorts the remaining unique city names alphabetically.

Concepts Covered

• DISTINCT
• ORDER BY
• ASC
• Sorting Unique Values

8. SQL Query to Display Unique Cities of Python Students

Problem Statement

Write an SQL query to display unique cities where students are enrolled in the Python course.

SQL Solution

SELECT DISTINCT city

FROM students

WHERE course = 'Python';

Sample Output

Explanation

The query first filters only students studying Python.

After filtering, DISTINCT removes duplicate city names.

Although two students from Delhi study Python, Delhi appears only once.

Concepts Covered

• DISTINCT
• WHERE
• Text Filtering

9. SQL Query to Display Unique Courses for Students Scoring More Than 85 Marks

Problem Statement

Write an SQL query to display all unique courses where students scored more than 85 marks.

SQL Solution

SELECT DISTINCT course

FROM students

WHERE marks > 85;

Sample Output

Explanation

The query filters students whose marks are greater than 85.

Then, DISTINCT returns only unique course names.

This type of query is useful for finding which courses have high-performing students.

Concepts Covered

• DISTINCT
• WHERE
• Unique Records

10. SQL Query to Display Unique Ages Greater Than 20

Problem Statement

Write an SQL query to display all unique ages greater than 20.

SQL Solution

SELECT DISTINCT age

FROM students

WHERE age > 20;

Sample Output

Explanation

The WHERE clause filters ages greater than 20, and the DISTINCT keyword removes duplicate age values.

Only unique ages satisfying the condition are displayed.

Concepts Covered

• DISTINCT
• WHERE
• Numeric Filtering
• Duplicate Removal

11. SQL DISTINCT with Multiple Columns and ORDER BY

Problem Statement

Write an SQL query to display all unique combinations of city and course, sorted alphabetically by city.

Sample Table

SQL Solution

SELECT DISTINCT city,
                course

FROM students

ORDER BY city ASC;

Sample Output

Explanation

The query first removes duplicate city-course combinations and then sorts the remaining records alphabetically by city.

This is useful for generating location-wise course reports.

Concepts Covered

• DISTINCT
• Multiple Columns
• ORDER BY
• ASC

12. SQL DISTINCT with DESC Sorting

Problem Statement

Write an SQL query to display all unique cities sorted in descending alphabetical order.

SQL Solution

SELECT DISTINCT city

FROM students

ORDER BY city DESC;

Sample Output

Explanation

The DISTINCT keyword removes duplicate city names.

The ORDER BY DESC clause arranges the remaining cities from Z to A.

Concepts Covered

• DISTINCT
• ORDER BY
• DESC
• Sorting Text Data

13. SQL Query to Display Unique Courses in Delhi

Problem Statement

Write an SQL query to display all unique courses available for students living in Delhi.

SQL Solution

SELECT DISTINCT course

FROM students

WHERE city = 'Delhi';

Sample Output

Explanation

The query first filters records where the city is Delhi.

Then, DISTINCT removes duplicate course names.

This helps identify all courses available in a particular location.

Concepts Covered

• DISTINCT
• WHERE
• Text Filtering

14. SQL Query to Display Unique Marks in Descending Order

Problem Statement

Write an SQL query to display all unique marks, sorted from highest to lowest.

SQL Solution

SELECT DISTINCT marks

FROM students

ORDER BY marks DESC;

Sample Output

Explanation

The query removes duplicate marks (if any) and sorts the remaining unique values in descending order.

This type of query is useful for:

• Score analysis
• Ranking systems
• Statistical reporting

Concepts Covered

• DISTINCT
• ORDER BY
• DESC
• Numeric Sorting

15. SQL DISTINCT Using Multiple Conditions

Problem Statement

Write an SQL query to display all unique cities where students:

• Study Python
• Scored more than 80 marks

SQL Solution

SELECT DISTINCT city

FROM students

WHERE course = 'Python'
AND marks > 80;

Sample Output

Explanation

This query combines:

• WHERE
• AND
• DISTINCT

SQL first filters students who satisfy both conditions:

• Course = Python
• Marks > 80

Finally, duplicate city names are removed using DISTINCT.

This type of query is commonly used in business analytics to identify unique locations based on multiple criteria.

Concepts Covered

• DISTINCT
• WHERE
• AND
• Multiple Conditions
• SQL Filtering

Chapter Summary

In this chapter, you learned how to use the SQL DISTINCT keyword to remove duplicate records from query results. The DISTINCT keyword is especially useful when working with large databases that contain repeated values.

You explored how to retrieve unique values from a single column, unique combinations from multiple columns, and how to combine DISTINCT with the WHERE and ORDER BY clauses to create more meaningful queries.

These techniques are widely used in data analysis, reporting, business intelligence, and database management.

Throughout this chapter, you covered:

• Introduction to the DISTINCT Keyword
• Removing Duplicate Values
• DISTINCT on a Single Column
• DISTINCT on Multiple Columns
• DISTINCT with WHERE
• DISTINCT with ORDER BY
• DISTINCT with Multiple Conditions
• Real-world SQL Examples

By mastering DISTINCT, you can generate cleaner reports and avoid duplicate information in your SQL query results.

Key Takeaways

• DISTINCT removes duplicate values from the result set.
• It works with both numeric and text data.
• It can be used on one or multiple columns.
• DISTINCT is applied after filtering with the WHERE clause.
• ORDER BY can sort the unique values returned by DISTINCT.
• Multiple columns with DISTINCT return unique combinations, not unique values for each column separately.
• DISTINCT improves report readability and data quality.
• It is commonly used in dashboards, analytics, and business reports.
• DISTINCT does not modify the original data in the table.
• It is one of the most frequently asked SQL interview topics.

Frequently Asked Questions (FAQs)

1. What is the SQL DISTINCT keyword?

The DISTINCT keyword removes duplicate values from the query result.

Example:

SELECT DISTINCT city

FROM students;

2. Does DISTINCT change the original table?

No.

DISTINCT only removes duplicate values from the query result. The actual data stored in the database remains unchanged.

3. Can DISTINCT be used with multiple columns?

Yes.

Example:

SELECT DISTINCT city,
                course

FROM students;

SQL returns only unique combinations of city and course.

4. Can DISTINCT be used with WHERE?

Yes.

Example:

SELECT DISTINCT city

FROM students

WHERE marks > 90;

The WHERE clause filters the data first, and then DISTINCT removes duplicate values.

5. Can DISTINCT be used with ORDER BY?

Yes.

Example:

SELECT DISTINCT city

FROM students

ORDER BY city ASC;

The query first removes duplicate cities and then sorts the remaining values alphabetically.

6. When should I use DISTINCT?

Use DISTINCT when you need:

• Unique cities
• Unique courses
• Unique departments
• Unique product categories
• Unique customer names
• Clean reports without duplicates

7. What is the difference between DISTINCT and GROUP BY?

• DISTINCT removes duplicate values from the result set.
• GROUP BY groups rows for aggregate calculations such as COUNT(), SUM(), AVG(), MIN(), and MAX().

Example:

SELECT DISTINCT course

FROM students;

Example using GROUP BY:

SELECT course,
       COUNT(*)

FROM students

GROUP BY course;

8. Where is DISTINCT used in real-world applications?

The DISTINCT keyword is commonly used in:

• Banking Applications
• Hospital Management Systems
• School and College Databases
• Customer Relationship Management (CRM)
• E-commerce Websites
• HR Management Systems
• Sales Dashboards
• Business Intelligence Reports
• Inventory Management Systems
• Data Analytics Projects

Written by Shubhranshu Shekhar, who has trained 20000+ students in coding.

Rishabh Kumar