equi-join

An equi-join, also known as an equijoin, is a specific type of comparator-based join, or theta join, that uses only equality comparisons in the join-predicate. Using other comparison operators (such as <) disqualifies a join as an equi-join. The query shown above has already provided an example of an equi-join:

SELECT *
FROM employee
INNER JOIN department
ON employee.DepartmentID = department.DepartmentID

SQL provides an optional shorthand notation for expressing equi-joins, by way of the USING construct (Feature ID F402):

SELECT *
FROM employee
INNER JOIN department
USING (DepartmentID