A database operation that combines some or all records from two or more tables. There are several types of joins:
An equi-join, which combines records from two tables whenever there are matching values in the joined fields.
An outer join, which includes all the records from one table and only those records from the second table in which the joined fields are equal.
A self-join, which is a table joined to itself. A self-join is useful when you ask hierarchical questions, such as a query that shows all the managers and the people who report to them.
You create a join with an SQL statement.