Hello again! I hope you enjoyed the previous unit on understanding and using the COUNT function. Today, we're going to expand your SQL knowledge further by introducing a new concept: the DISTINCT keyword in SQL. While DISTINCT is not strictly speaking a function it's a powerful keyword/clause that will help you strengthen your data querying skills.

When handling data, especially large datasets, we often encounter duplicate values. The DISTINCT keyword helps us remove these duplicates and present a clean, unique list of values. Isn't that handy?!

This concept is common in many areas of life. Imagine you're trying to create a list of all the cities from which your friends come. If three friends come from New York, should we count New York three times? Of course not! We use distinct or unique values, and SQL provides the DISTINCT keyword to do just that with our data.

As we learn SQL using Messi's matches, we'll be using DISTINCT to explore his distinct sport footprints.

Given Lionel Messi's rich game history, utilizing DISTINCT is quite handy. We can use it to identify unique seasons, and much more. It will broaden our understanding of his matches data.

Let's first learn the format of a basic SQL query that uses DISTINCT.

SQL
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1SELECT DISTINCT column_name FROM table_name;

It is time to apply this format to our Lionel Messi's matches dataset. Consider the following statement:

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1SELECT DISTINCT season_id FROM Matches;
2
3-- Sneak peek of the output:
4--  season_id
5-- -----------
6--          1
7--          2

This query will fetch all the distinct or unique season_id from the Matches table. We use DISTINCT to avoid getting repeated IDs in the output.

Let's look at a few more examples using the DISTINCT keyword.

What if we want to know all the unique clubs Messi has played for? Simple, we would run:

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1SELECT DISTINCT club_id FROM Matches;
2
3-- Output:
4--  club_id
5-- ---------
6--        1
7--        2

When using DISTINCT, it's important to remember that fetching unique values from large datasets can be time-consuming and slow down your queries. Therefore, always consider the performance implications and use DISTINCT only when necessary.

That wraps up our introduction to the DISTINCT keyword in SQL! Well done on expanding your SQL toolkit. Today, you learned to use DISTINCT to fetch unique values from a database, which is handy in many data analysis scenarios. We also explored how distinct can be applied to Lionel Messi's data for deeper insights.

Now, it's time to apply your newfound knowledge in practice! Next up, you'll be tackling some hands-on exercises using DISTINCT with the Lionel Messi dataset. Happy coding!