How get one line per key in left outer join - sql-server

Question

The context is a transaction table with date and UserAccount. This table contains about billion lines.
dOperationValueDate sUserAccount
------------------- ----------------------------------------------
2016-03-05 00000000001
2016-03-06 00000000002
2016-03-07 00000000003
2016-03-08 00000000004
2016-03-09 00000000005
2016-04-05 00000000002
2016-10-05 00000000001
2016-10-06 00000000001
2016-10-06 00000000005
I would like to find datas in my table with these criterias :
At least one transaction before 6 months ago (like TOP 1 *)
No transaction for 6 months
In my example, the results would be accounts 2, 3, 4.
I started with a LEFT OUTER JOIN, in order to remove all userId with transaction since 6 months. But the processing time is just horrible : for 4 hours right now.
SELECT b.sUserAccount FROM
(SELECT sUserAccount FROM T_Operations WITH (readuncommitted) WHERE dOperationValueDate < DATEADD(month, -6, DATEADD(month, DATEDIFF(month, 0, GETUTCDATE()), 0)) GROUP BY sUserAccount) b -- all operations before 6 months ago
LEFT JOIN
(SELECT sUserAccount FROM T_Operations WITH (readuncommitted) WHERE dOperationValueDate >= DATEADD(month, -6, DATEADD(month, DATEDIFF(month, 0, GETUTCDATE()), 0)) GROUP BY sUserAccount) c -- all operations since 6 months
ON b.sUserAccount = c.sUserAccount
WHERE c.sUserBankAccount IS NULL) d -- remove all customers who have operations before 6 months ago and since 6 months / keep only customers who have operations beofre 6 months ago only
I think the solution is to find only one operation in the b query, and sql stops when it find one row. The main problem is only if the user doesn't have transaction before 6 months ago but for the others, it will be fine.
On the other hand, I have to check each transaction since 6 months in order to remove customers from the scope.
I read about CROSS APPLY, but I'm not sure about how it works.
The main problem here is the processing time. I have to do a "quick" request (less than 1 hour).

Answer 1

I think you should be able to just use NOT EXISTS here.
SELECT b.sUserAccount
FROM T_Operations b WITH (READUNCOMMITTED)
WHERE b.dOperationValueDate < DATEADD(month,-6,DATEADD(month,DATEDIFF(month,0,GETUTCDATE()),0))
AND NOT EXISTS ( SELECT 1
FROM T_Operations WITH (READUNCOMMITTED)
WHERE sUserAccount = b.sUserAccount
AND dOperationValueDate >= DATEADD(month,-6,DATEADD(month,DATEDIFF(month,0,GETUTCDATE()),0)) )
GROUP BY b.sUserAccount -- all operations before 6 months ago
or actually, you might be able to just use GROUP BY with HAVING
SELECT sUserAccount
FROM T_Operations WITH (READUNCOMMITTED)
GROUP BY sUserAccount
HAVING MAX(dOperationValueDate) < DATEADD(month,-6,DATEADD(month,DATEDIFF(month,0,GETUTCDATE()),0))
as a side note.. DATEADD(month,-6,DATEADD(month,DATEDIFF(month,0,GETUTCDATE()),0)) would return 2016-04-01
if you want current date, minus six months you can use DATEADD(month,-6,CAST(GETUTCDATE() AS DATE)) or DATEADD(month,-6,DATEADD(day,DATEDIFF(day,0,GETUTCDATE()),0)

Answer 2

datatime #dt = DATEADD(month, -6, DATEADD(month, DATEDIFF(month, 0, GETUTCDATE()), 0));
SELECT sUserAccount
FROM T_Operations WITH (readuncommitted)
WHERE dOperationValueDate < #dt
EXCEPT
SELECT sUserAccount
FROM T_Operations WITH (readuncommitted)
WHERE dOperationValueDate >= #dt;
Have an index on dOperationValueDate