Introduction to SQL JOINs

SQL JOINs are a fundamental concept in SQL and are used to combine data from two or more tables based on a related column between them. This allows you to retrieve data from multiple tables as if it was stored in a single table.

There are several types of SQL JOINs, each with its own syntax and use case. The most common types of SQL JOINs are INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN.

The INNER JOIN keyword selects only the rows where there is a match in both tables. The LEFT JOIN keyword returns all records from the left table (table1), and the matched records from the right table (table2). The RIGHT JOIN keyword returns all records from the right table (table2), and the matched records from the left table (table1). The FULL OUTER JOIN keyword returns all records when there is a match in either left (table1) or right (table2) table records.

To perform a SQL JOIN, you use the JOIN keyword and specify the columns that link the tables. For example, if you have two tables "customers" and "orders", you can join them based on a related column "ID" as follows:

1SELECT *
2FROM customers
3JOIN orders
4ON customers.ID = orders.ID;