SELECT *
FROM employee INNER JOIN department
ON employee.DepartmentID = department.DepartmentID;
The following example shows a query which is equivalent to the one from the previous example.

SELECT *
FROM   employee, department
WHERE  employee.DepartmentID = department.DepartmentID;

Outer joins

  An outer join does not require each record in the two joined tables to have a matching record. The joined table retains each record—even if no other matching record exists. Outer joins subdivide further into left outer joins, right outer joins, and full outer joins, depending on which table(s) one retains the rows from (left, right, or both).

Example of a left outer join, with the additional result row italicized:

SELECT *
FROM   employee  LEFT OUTER JOIN department
ON employee.DepartmentID = department.DepartmentID;

Example right outer join, with the additional result row italicized:

SELECT *
FROM   employee RIGHT OUTER JOIN department
ON employee.DepartmentID = department.DepartmentID;

Example full outer join: åQˆmysql is not supportåQ?/p>

SELECT *
FROM   employee
FULL OUTER JOIN department
ON employee.DepartmentID = department.DepartmentID;

Self-join

An example solution query could be as follows:

SELECT F.EmployeeID, F.LastName, S.EmployeeID, S.LastName, F.Country
FROM Employee F, Employee S
WHERE F.Country = S.Country
AND F.EmployeeID < S.EmployeeID
ORDER BY F.EmployeeID, S.EmployeeID;

Which results in the following table being generated.

Join algorithms

Three fundamental algorithms exist for performing a join operation: Nested loop join, Sort-merge join and Hash join.