What tasks can be solved using the JOIN operation in SQL?

The JOIN operation in SQL is used to combine rows from two or more tables based on a related column between them. The main tasks that can be solved using JOIN:

• Combining data from related tables. The primary task that allows obtaining a complete set of information distributed across different tables. For example, getting a list of orders with product names and customer names.
• Filtering data based on relationships. JOIN can be used together with WHERE conditions to select data that meets certain criteria in related tables.
• Analyzing relationships between entities. It helps understand how data in one table is related to data in another.
• Creating reports. JOIN is fundamental for building reports that combine information from various parts of a database.
• Ensuring data integrity. In some cases, albeit indirectly, JOIN can be used to verify the existence of related data before performing modification operations.

Different types of JOIN address specific combination tasks:

• INNER JOIN: Returns only the rows where there are matches in both tables.
• LEFT JOIN (LEFT OUTER JOIN): Returns all rows from the left table and matching rows from the right table. If there are no matches, the results from the right table will be NULL.
• RIGHT JOIN (RIGHT OUTER JOIN): Returns all rows from the right table and matching rows from the left table. If there are no matches, the results from the left table will be NULL.
• FULL JOIN (FULL OUTER JOIN): Returns all rows from both tables. If there are no matches, the results in the respective table will be NULL.
• CROSS JOIN: Returns the Cartesian product of the rows of the two tables (each row of the first table is combined with each row of the second). It is used less frequently to obtain all possible combinations.

Example of a query using INNER JOIN:

SELECT o.orderId, c.customerName, p.productName
FROM Orders o
INNER JOIN Customers c ON o.customerId = c.customerId
INNER JOIN Products p ON o.productId = p.productId;