Question

Let’s say I have three tables:

LOCATIONS – a store can belong to multiple locations and a location can have multiple stores

+-------------+----------+
| LOCATION_ID | STORE_ID |
+-------------+----------+

STORES – only one row per store, every store has only one manager ID

+----------+------------+
| STORE_ID | MANAGER_ID |
+----------+------------+

EMPLOYEES – a manager can have multiple employees, and employees can belong to more than one manager

+-------------+-------------+
| MANAGER_ID  | EMPLOYEE_ID |
+-------------+-------------+

And for a given location (e.g. LOCATION_ID = 999), I want to get all the employees managed at stores at that location.

This gets me the list of managers that belong to stores in that location:

SELECT s.MANAGER_ID FROM LOCATIONS l
  INNER JOIN STORES s 
     ON s.STORE_ID = l.STORE_ID 
  WHERE l.LOCATION_ID = 999;

What I actually want is ALL the distinct EMPLOYEE_IDs that are linked to the managers that query spits out.

What additional join can I add in the same query to get that?

Answer 1

SELECT DISTINCT E.EMPLOYEE_ID 
FROM LOCATIONS L  
INNER JOIN STORES S ON S.STORE_ID = L.STORE_ID   
INNER JOIN EMPLOYEES E ON S.MANAGER_ID = E.MANAGER_ID 
WHERE L.LOCATION_ID = 999;