correlated sub query

It is a query nested inside another query.

http://en.wikipedia.org/wiki/Correlated_subquery


Scenario: Write a query to select all employees from eastern region. DB diagram follows:

--select all employees from Eastern region
select * from employees where EmployeeID in
(
    -- select all Employees under territory which comes under Eastern region
    select EmployeeID from employeeterritories where TerritoryID in
    (
        --select all territory for Easter region (RegionID = 1)
        select TerritoryID from territories where RegionID = 1
     )
 )