DISTINCT — Complete Guide
DISTINCT — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of SQL Server Tutorial on Toolliyo Academy.
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SQL Server Tutorial · Lesson 16 of 100
DISTINCT
SQL basics → Queries → Advanced
SQL basics · 1 — SELECT · ~6 min · SQL — SQL Queries & Clauses
What is this?
DISTINCT removes duplicate rows from the result. It compares the whole selected row, not one column in isolation unless you select only that column.
Why should you care?
You need the list of cities that ordered — not every order row. DISTINCT (or GROUP BY) gives unique values.
See it live — copy this example
Run in SQL Server Management Studio (SSMS) or Azure Data Studio.
USE DataVerse;
SELECT DISTINCT City
FROM dbo.Orders
ORDER BY City;
SELECT City, COUNT(*) AS RowsSeen
FROM dbo.Orders
GROUP BY City; -- often clearer when you also need countsWhat happened?
- First query returns each City once.
- Second shows the GROUP BY alternative when you care about counts too — prefer that over DISTINCT + separate count.
Practice next
- Insert another Pune order and rerun DISTINCT City.
- SELECT DISTINCT City, Amount and see more rows.
- Compare DISTINCT vs GROUP BY City.
- SELECT DISTINCT LEFT(City, 3) AS CityPrefix.
- COUNT(DISTINCT City) in a single aggregate query.
Remember
DISTINCT collapses duplicate result rows. GROUP BY is better when aggregating. Fix JOIN fan-out instead of masking it.
Unique delivery cities
Logistics loads DISTINCT City from DataVerse Orders for route planning.
Outcome: City dropdown stays clean without duplicates.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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