What does a LEFT JOIN do in SQL?

A LEFT JOIN in SQL is designed to retrieve all records from the left table, regardless of whether there are matching records in the right table. When a LEFT JOIN is performed, it ensures that every record from the left table is included in the result set, and if there is a corresponding match found in the right table, the relevant information from that table is also included. If no match exists, the result will still include the record from the left table, but the fields from the right table will display NULL values.

This behavior is especially useful when you want to ensure that you don't miss out on any data entries from the left table, such as tracking all customers and their orders, even if some customers have not placed any orders. By utilizing a LEFT JOIN, data analysts and database users can effectively handle situations where the relationship between the two tables may be one-to-many or one-to-zero.

In contrast, other types of joins may limit the results to only those rows where there is a match in both tables or rely on conditions that help filter results post-aggregation, which is not the purpose of a LEFT JOIN. Thus, the characteristic of returning all records from the left table while including matched records from the right table makes the LEFT JOIN a powerful tool