Joins

Joins are the primary mechanism in SQL for combining rows from two or more tables based on a related column between them. While we've touched on them before, this topic delves into the specific types. The most common is the `INNER JOIN`. It returns records that have matching values in both tables. If a row in Table A has no corresponding match in Table B (based on the join condition), it is excluded from the result. A `LEFT JOIN` (or `LEFT OUTER JOIN`) returns all records from the left table (Table A), and the matched records from the right table (Table B). If there is no match for a record from the left table, the result is `NULL` on the right side. This is useful for finding records in one table that do not have a corresponding record in another, such as finding all customers who have never placed an order. A `RIGHT JOIN` (or `RIGHT OUTER JOIN`) is the mirror image of a left join. It returns all records from the right table (Table B), and the matched records from the left table (Table A). If there is no match, the result is `NULL` on the left side. A `FULL OUTER JOIN` returns all records when there is a match in either the left or the right table. It combines the functionality of both `LEFT JOIN` and `RIGHT JOIN`. It's useful for seeing all data from both tables and where they are related. Understanding which join to use in a given scenario is a critical SQL skill.