Greetings, and welcome to our second unit in the "Learning SQL with Leo Messi" course!

You have already journeyed through what databases are, explored the world of SQL, and understood the usage of MySQL. Remember how we wrote our first SHOW TABLES SQL command to list all the tables in a Messi database? That was your first step into SQL syntax!

SQL, unlike many programming languages, doesn't deal with logic or flow control; instead, it understands, manipulates, and retrieves data stored in databases in a structured manner.

In this lesson, we will cover the SELECT keyword. The syntax is straightforward.

General Syntax:

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1SELECT column1, column2, ..., columnN FROM table_name

In this syntax, you mention the column names that you want to retrieve, separated by commas. If you want to retrieve all columns, replace the column names with an asterisk (*).

Let's see how it works!

Let's pull all the data from the Clubs table. We'll use the asterisk (*) symbol to do this.

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1SELECT * FROM Clubs;

This statement fetches all columns, along with their data, from the table Clubs. You would see club_id, club_name, club_country, and more, all displaying data from the Lionel Messi's clubs table.

Now, what if we want only specific information, such as the club name and club country? It's simple. We replace the asterisk with the required column names. Here's how:

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1SELECT club_name, club_country FROM Clubs;

In this example, we have fetched only the club_name and club_country columns from our Clubs table. Isn't fine-tuning our query results exciting?

Can we rename column names in the output for better understanding? Yes, we can! Thanks to SQL aliasing features. The AS keyword is used to rename a column or table with an alias.

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1SELECT club_name AS Name, club_country AS "Club Country" FROM Clubs;

In this statement, AS is used to rename club_name to Name and club_country to Club Country in our output. Notice that we use double quotes around Club Country because the new name contains spaces. This way, our result set has more comprehensible column names.

The output of this query would be:

Let's recap what we've covered:

• SELECT * FROM Clubs will fetch all columns.
• SELECT club_name, club_country FROM Clubs will fetch specific columns.
• SELECT club_name AS Name, club_country AS "Club Country" FROM Clubs will fetch specific columns and rename them in the output.

Practice these commands with different columns and aliases to gain a firm understanding of the SELECT statement. Don't worry if you make mistakes — they are stepping stones to mastering any new skill. Let's get to practice.

That wraps up our second unit! You now understand the SQL syntax, the SELECT command, and the usage of the AS keyword to rename items in the output of your query.

The practice exercises that follow this lesson will further reinforce these concepts. Remember, the best way to learn is by doing. So, try writing and running your own SQL commands before you move on to the practice exercises.

Great job so far, and keep practicing!