Su majestad el SELECT

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Why is "Select" fundamental in databases?

Throughout the development of applications and business processes, managing databases is inevitably crucial. This is where "Select" comes into play, which is the most important modular tool in the MySQL context. Thanks to "Select", we can extract specific data from the database, which is vital for making informed decisions and efficiently managing information. Regardless of how we store data, at the end of the day, we need to know how to take that data and transform it into valuable information.

How do you select specific columns?

If we want to see all the information in a table of users, we can use:

SELECT * FROM customers;

This command gives us all the tuples and columns in the table. However, it is often not practical to bring all this information.

If we only need certain fields, we can specify:

SELECT name, email, gender FROM clients;

This will allow us to focus on the specific columns we are interested in and better manage the amount of data we receive.

When and how to use "LIMIT" in queries?

There are occasions when we only want to see a part of the data. Here the reserved word "LIMIT" is useful, which allows us to restrict the number of rows that our "Select" returns. For example:

SELECT name, email, gender FROM clients LIMIT 10;

This gives us the first ten rows of the query, regardless of the order of the data. It is a quick way to preview the structure and content of the data without being overwhelmed with information.

How to apply conditions to queries?

To further simplify queries and get more specific data, conditions are used. The "WHERE" clause is key to this:

SELECT * FROM clients WHERE gender = 'M';

Here, only records where the gender is male will be returned. This technique helps us filter results based on specific criteria.

How to use functions in queries?

Functions in MySQL are powerful tools to transform and manipulate data directly in our queries. For example, if we want to get only the year of birth of each customer:

SELECT YEAR(birth_date) FROM clients;

This extracts the year of each birth date. Also, by combining functions we can perform simple calculations, such as determining the age of each person:

SELECT name, YEAR(NOW()) - YEAR(birth_date) AS age FROM clients;

The YEAR(NOW()) function subtracts the year of birth of each client, providing an approximate view of age.

What is "LIKE" and how is it used for partial matches?

If we want to find data based on partial matches, the "LIKE" function is invaluable. For example:

SELECT * FROM clients WHERE name LIKE '%Pablo%';

With this query, we search for any client whose name contains the string "Pablo". The symbol % acts as a wildcard representing any sequence of characters, before or after "Pablo".

How do you combine conditions and functions in queries?

For more complex queries, we can combine multiple conditions and functions. For example, to find women whose name includes "Lopez" and also their email and age, we can type:

SELECT name, email, YEAR(NOW()) - YEAR(birth_date) AS age, genderFROM clientsWHERE gender = 'F' AND name LIKE '%Lopez%';

This advanced query type shows how to take advantage of SQL's flexibility to extract valuable information efficiently.

Why is it important to design optimized queries?

Optimal query design is crucial to database performance, especially when handling large volumes of data, such as millions of users. By creating non-exhaustive but effective queries, we optimize the use of resources and ensure fast responses, even in very large databases. Mastering this art allows us to make quick and efficient decisions based on complex data sets.

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