>>Goal: To get all accounts that have purchased a specific product more then one month ago but have *not* purchased within the last month.
>>
>>I've tried the following but it's very slow where a lot of accounts have purchased the product in the last month:

WITH Temp_CTE (AccountCode,InvoiceDate)
>>AS
>>(
>>SELECT SI.AccountCode,MAX(SI.InvoiceDate) FROM SalesInvoiceItem IV 
>>INNER JOIN SalesInvoice SI ON IV.InvoiceNumber = SI.InvoiceNumber
>>WHERE ProductCode='56.GTR003.001.01' AND SI.InvoiceDate >= DATEADD(MONTH, - 1,GETDATE())
>>GROUP BY SI.AccountCode
>>)
>>SELECT SI.AccountCode,MAX(SI.InvoiceDate) AS Latest  FROM SalesInvoiceItem IV 
>>INNER JOINSalesInvoice SI ON IV.InvoiceNumber = SI.InvoiceNumber
>>LEFT JOIN Temp_CTE ON SI.AccountCode = Temp_CTE.AccountCode
>>WHERE ProductCode='56.GTR003.001.01' AND SI.InvoiceDate < DATEADD(MONTH, - 1,GETDATE()) AND Temp_CTE.AccountCode IS NULL
>>GROUP BY SI.AccountCode

>>
>>I'm useless at SQL - can anyone suggest a way of speeding this up?
>
>
>From which table ProductCode comes from?

From SalesInvoiceItem, but it should have an alias of IV.