MS Access One-to-Many Query - sql

Question

I'm working on a service type database. Customers can have many equipment types and many service calls.
I'm trying to make a query that selects the customers name, address, etc when certain parameters are met with relation to the equipment types.
A customer can have upto 5 different equipment types. Some only have 1, some have all 5.
My query is trying to find customers with equipment type 3 installed, but not equipment type 5. The equipment type 3 must also have a service date between to date fields on my search form.
I'm drawing a blank when it comes to writing this query. I was able to query the customers with equipment type 3 and specific service dates, but I can't seem to be able to eliminate the customers that also have equipment 5 installed, even if they also have equipment type 3 installed.
This is my SQL:
SELECT
tblCustomers.WCWF_ID,
tblCustomers.CustBusiness,
tblCustomers.CustLastName,
tblCustomers.CustFirstName,
tblCustomers.CustAddress,
tblCustomers.CustCity,
tblCustomers.CustST,
tblCustomers.CustZip5,
tblEquip.EquipResinDate,
tblEquip.EquipType,
tblCustomers.CustPostCard
FROM
tblCustomers
INNER JOIN
tblEquip ON tblCustomers.WCWF_ID = tblEquip.WCWF_ID
WHERE
(((tblEquip.EquipResinDate) Between [forms]![MailSearchSelect]![StartDate] And [forms]![MailSearchSelect]![EndDate])
AND ((tblEquip.EquipType)=3
AND (tblEquip.EquipType)<>5)
AND ((tblCustomers.CustPostCard)=True));
Any help would be greatly appreciated.

Answer 1

The problem with your query is that you are tying to use a single JOIN to filter in customers with equipment type 3 and filter out customers with equipment type 5 : you would need to split that logic into two distinct parts.
To pull out customers that have equipment type 3 installed, using a JOIN is fine (I just moved the related conditions from the WHERE clause to the JOIN, for more clarity). It would also have been possible to express this requirement as a WHERE EXISTS condition with a correlated subquery.
To exclude customers that have equipment type 5 installed, you can either :
use a NOT EXISTS condition in the WHERE clause with a correlated subquery (I chose that option)
or use a LEFT JOIN with WHERE ... IS NULL.
Query :
SELECT
c.WCWF_ID,
c.CustBusiness,
c.CustLastName,
c.CustFirstName,
c.CustAddress,
c.CustCity,
c.CustST,
c.CustZip5,
e.EquipResinDate,
c.EquipType,
c.CustPostCard
FROM
tblCustomers AS c
INNER JOIN tblEquip AS e
ON e.WCWF_ID = c.WCWF_ID
AND e.EquipType = 3
AND e.EquipResinDate
BETWEEN [forms]![MailSearchSelect]![StartDate]
AND [forms]![MailSearchSelect]![EndDate])
WHERE
c.CustPostCard = True
AND NOT EXISTS (
SELECT 1
FROM tblEquip AS e2
WHERE
e2.WCWF_ID = c.WCWF_ID
AND e2.EquipType = 5
)
PS : it is also a good idea to give alias to the table names ; it makes the query more readable and may avoid subtle bugs caused by name clashes when the same table is referenced more than once in the query.