Query to find customers who have not purchased anything

Question

I have a query to find customers who have purchased what we call consumables (using item property) over a given period:
SELECT T0.CardCode, T0.CardName, T0.DocDate, T0.DocTotal, T1.ItemCode, T1.Dscription,T1.quantity, T2.ItmsGrpNam
FROM OINV T0  INNER JOIN INV1 T1 ON T0.DocEntry = T1.DocEntry, OITG T2
WHERE T0.DocDate BETWEEN '[%0]' AND '[%1]' AND T1.ItemCode like '2ssy%' AND  T2.ItmsGrpNam = 'consumable'
I have another to show customers who have a particular type of equipment:
SELECT T0.manufSN,T0.itemName,  T3.Name, T2.Address, T2.Street, T2.Block, T2.City, T2.County, T2.ZipCode
FROM OINS T0 INNER JOIN OCRD T1 ON T0.customer = T1.CardCode INNER JOIN CRD1 T2 ON T1.CardCode = T2.CardCode Inner Join OCPR T3 ON T0.ContactCod = T3.CntctCode
WHERE T0.manufSN like 'P%' AND T2.AdresType= 'S'
What I would like is to find those customers who have this equipment (query 2) but who have NOT purchased and consumables in say the last year.
I have tried using Excel by finding duplicates and taking those in query 1 from those in query 2 but it's very messy.
Has anyone done anything like this or got any good ideas?
Thanks

Answer 1

Hi Ralph,
Well, I enjoy teaching, so let's start at the beginning.  SQL is a fairly full-featured language, and it supports recursion and nesting.  That's why the books online often describe elements of the SQL statements as "expression" - it may be more than a field or a simple function occurring there.  Nesting is the little puppy we used here.
Now, in your first post, you said:  "What I would like is to find those customers who have this equipment (query 2) but who have NOT purchased and consumables (query 1) in say the last year."
So, our common point between the two queries is the customer, the CardCode.  That's what this part does:  F0.CardCode = T0.Customer.  In my internal convention, I used F for Filter.  So we only want the results in the filter where the CardCode matches the CardCode/Customer from the main query tables.  It's the sole contact point between the two queries.
You also said you wanted only the items where they had purchased no consumables, which basically translates into: a count of the records equals 0.  Now, since all we're interested in from the second query, the consumables query is how many records we returned, we get rid of all the columns except for one that we apply a COUNT to.  After that, it's a simple criteria:  the result of the second query has to equal 0.  This is how the criteria looks after you take out all the details and put only the important brackets in:  (SELECT COUNT...FROM...WHERE...) = 0.
This might be confusing at first, because most of the time we return recordsets from queries, but a standard feature of SQL is to return a value of any data type if the query returns a single row and a single column.  This wouldn't work at all if we had more than one column in our nested query (or would require lots of tweaking), and although it returns a number of results in the complete process of the whole SQL statement, it only returns one result for each row.
Regards,
Mark Dielmann
Edited by: Mark Dielmann on Nov 13, 2009 12:30 PM - Forum doesn't support advanced formatting on answered questions.
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