Question

Using an MS Access database with the following design:

Tables
Equipment, Employees, CreditCard

Fields
Equipment: ID, PrimaryEmployee, SecondaryEmployee
Employees: ID, CreditCard
CreditCard: ID, Number, Pin

So, a piece of equipment can have two different employees assigned to it. Each employee can have a CreditCard assigned to them, or not at all.

Based on the ID of a piece of Equipment:

• If the piece of equipment has a SecondaryEmployeeID set, and that
  corresponding Employee has a CreditCard set, then return the value of
  that CreditCard.
• Else If the piece of equipment has a PrimaryEmployeeID set, and that
  corresponding Employee has a CreditCard set, then return the value of
  that CreditCard.

I also have to pull the employee’s name from the Employees table in the same query, and thus, I was using a LEFT JOIN before, which seemed to make it impossible to do this in my knowledge.

EDITED

My current query attempt:

SELECT
    Equipment.ID,
    Equipment.PrimaryEmployee,
    Equipment.SecondaryEmployee,
    Employees.CreditCard,
    CreditCard.Pin
FROM
    (Equipment
        LEFT JOIN Employees ON Equipment.PrimaryEmployee = Employees.ID
    )
LEFT JOIN CreditCard ON Employees.CreditCard = CreditCard.ID
WHERE (((Equipment.EquipmentType)=1))

I removed some unrelated fields from the query to hopefully improve readability, and simplify the area I’m having troubles.

This is currently generating a result like:

ID    PrimaryEmployee    SecondaryEmployee    CreditCard    Pin
--------------------------------------------------------------------
1     John Doe           Jack Smith           1234567890    1234
2     Bubba Smith        Ryan Howard          2345678901    2345

The problem is that it only matches on the PrimaryEmployee. I need it to check the SecondaryEmployee first, and if that doesn’t have a match or credit card set, then match on the PrimaryEmployee. If neither match, then return Null or ‘-‘.

Let me know if additional information is still required.

Answer 1

The easiest way to do this, without mucking up the SQL, is to create a second query that uses the results from your first query and pulls in the Employee column where your first result IS NULL.

Once you’ve got your two queries, you’re just a stone’s throw from writing a third query that joins the results from both queries into a single output.