What's faster, SELECT DISTINCT or GROUP BY in MySQL?

Detailed reasoning

Run time evaluation

When dealing with one value, the more streamlined SELECT DISTINCT operation is often faster. It behaves like a surgical knife, excising duplicates without bogging down the query optimizer. It’s like asking your sibling to fetch your keys, precise and simple.

Keep an eye on those MySQL versions; as each update brings about change in how the optimizer works, make sure to utilize EXPLAIN for the latest insights.

But wait, GROUP BY isn't just an extra wheel. It shines when there's an index on the unique column, transforming to a pretty fast racer when juggling larger datasets.

Unique columns

The waters get murky when handling multiple columns. SELECT DISTINCT zeroes in on uniqueness across all columns, making laser-like precise cuts. However, GROUP BY can be turned into a swiss knife, allowing you to tweak with aggregate functions for greater flexibility.

In these scenarios, visualizing the expected outcome is as important as tasting the broth while cooking. Testing actual scenarios with representative data is a surefire way to avoid a rude shock at runtime.

Indexing: A Developer's best friend

Whether it's DISTINCT or GROUP BY, indexing turbocharges the query. It's like adding more lanes to our SQL highway, letting the data flow smoothly. If you're grouping data, consider marking columns as "frequently used" with an index to quench your need for speed.

Overhead costs

SELECT DISTINCT is like a small electric car — does one job well with minimum fuss. It gently plucks out the duplicates, avoiding the need for any heavy lifting. If your task is to simply retrieve a list of unique values, this is your go-to approach.

Adjust to your goals

The best approach isn't written in stone. It morphs to fit your specific use case like pliable dough. The key is to look at the context and pick the one that aligns with your end objective.

Delving into methods

Targeting precisely

Does your use case scream "Simplicity!"? SELECT DISTINCT can be the perfect tool. Lovely for seizing unique values in a list, SELECT DISTINCT skirts the complex joins and keeps it light.

-- Quick and dirty. Like a simple "Hi!" instead of a long handshake.
EXPLAIN SELECT DISTINCT column_name FROM column_name;
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However, don't let it fool you! Like a lazy cat, it might just sprawl over your entire table without using the index. Keep checking on the execution plan.

Handling bulk data

When your queries are more complex, GROUP BY dances like a champ. It excels for data categorization, aggregation and works splendidly well when an order is required.

-- Handling your heavy stuff like a Gym bro. Flex those muscles, GROUP BY!
EXPLAIN SELECT column_name, COUNT(*) FROM table_name GROUP BY column_name;
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There's a trick under its sleeve as well. An index on the group columns can significantly cut down query times. Use it!

The real-deal testing

Your data, your choices

The choice can swing either way. So pick up your data and put it to the test. Particularly for larger data, the fine-grained performance analysis can provide a solid foundation for your decision.

-- Because every superhero needs a training regimen. Train those queries!
Benchmark(batch_dl_query_on_your_own_dataset)
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Outcome in the eye of the storm? Make sure the queries are readable and maintainable. It may seem a small detail today, but future you will thank you!