“Distinct vs Group By in SQL Server” (2024)

Smita Gudale

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Dec 5, 2019

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SQL COUNT() with GROUP by - w3resource

DISTINCT-

DISTINCT is used to filter unique records out of all records in the table. It removes the duplicate rows.

SELECT DISTINCT will always be the same, or faster than a GROUP BY.

• In the following table duplicate records are present.

• Now I am applying a DISTINCT and GROUP BY clause on StudentName Column. It will produce the same outputs.

• The SQL Server query optimizer produces the same plan for both the queries as shown below.

GROUP BY-

The GROUP BY clause is used to group a selected set of rows into summary rows by one or more columns or an expression.

The group gives the same result as distinct when no aggregate function is present.

GROUP BY is required if you’re aggregating data, but in many cases, DISTINCT is simpler to write and read if you aren’t aggregating data.

• In the following query, I use COUNT function with a group by-

The major difference between the DISTINCT and GROUP BY is, GROUP BY operator is meant for the aggregating or grouping rows whereas DISTINCT is just used to get distinct values.

If you are new to SQL Server start with the following must-watch video: -

I'm an experienced SQL enthusiast with a deep understanding of database management systems, particularly in the context of SQL Server. My expertise is grounded in practical experience, and I've consistently demonstrated a comprehensive knowledge of SQL concepts and their effective application.

In the provided article by Smita Gudale, she discusses the use of DISTINCT and GROUP BY clauses in SQL Server to filter unique records and aggregate data. Let's break down the concepts used in the article:

1. DISTINCT:

   • Purpose: DISTINCT is used to filter unique records from all records in a table, removing duplicate rows.
   • Performance: The article mentions that SELECT DISTINCT will always be the same or faster than a GROUP BY operation.
   • Example: Applying DISTINCT on the StudentName column produces the same output as using GROUP BY.

2. GROUP BY:

   • Purpose: GROUP BY is used to group a selected set of rows into summary rows based on one or more columns or an expression.
   • Similarity to DISTINCT: When no aggregate function is present, GROUP BY provides the same result as DISTINCT.
   • Aggregation: GROUP BY is required when aggregating data. However, DISTINCT is simpler to write and read when aggregation is not needed.
   • Example: The article demonstrates using the COUNT function with GROUP BY for aggregating data based on certain criteria.

3. Query Optimization:

   • The article mentions that the SQL Server query optimizer produces the same plan for both DISTINCT and GROUP BY queries when applied to the same dataset.

4. Difference between DISTINCT and GROUP BY:

   • The major distinction highlighted is that the GROUP BY operator is meant for aggregating or grouping rows, while DISTINCT is used solely to retrieve distinct values.

5. Learning Resource:

   • The article suggests that beginners start with a must-watch video for those new to SQL Server.

In summary, this article provides valuable insights into the practical use of DISTINCT and GROUP BY in SQL Server, emphasizing their similarities, differences, and performance considerations. It also directs beginners to a recommended learning resource, contributing to a holistic understanding of SQL concepts and their application.