Dynamic WHERE or conditional JOIN?

Question

I have a 3 table join that I need to filter in either of two ways depending on row data. Initially I had the following select statement:
SELECT Warnings.WarningID, Subscriptions.UserID, Accounts.AccountName, Accounts.Ask, Warnings.Direction, Warnings.Rate, Warnings.Active
FROM Warnings INNER JOIN
Subscriptions ON Warnings.SubscriptionID = Subscriptions.SubscriptionID INNER JOIN
Accounts ON Subscriptions.AccountID = Accounts.AccountID
WHERE (Warnings.Active = 1)
My problem is to filter this further. Warnings.Direction is a bit where 0 means '<' and 1 means '>' and is meant to be used to differentiate between 'Accounts.Ask > Warnings.Rate' and 'Accounts.Ask < Warnings.Rate' so that I can select whatever
is relevant for each row.
I went through a series of failed attempts focusing on the WHERE clause, but then I tried the Design Query Editor and it produced a condition JOIN instead. The closest I've come so far is this is this:
SELECT Warnings.WarningID, Subscriptions.UserID, Accounts.AccountName, Accounts.Ask, Warnings.Direction, Warnings.Rate, Warnings.Active
FROM Warnings INNER JOIN
Subscriptions ON Warnings.SubscriptionID = Subscriptions.SubscriptionID INNER JOIN
Accounts ON Subscriptions.AccountID = Accounts.AccountID AND Accounts.Ask < Warnings.Rate
WHERE (Warnings.Active = 1)
which at least filters correctly for '<'. Is it possible to update this maybe with a CASE statement so that the conditional JOIN can tackle either Warnings.Direction option? Something along the lines of:
SELECT Warnings.WarningID, Subscriptions.UserID, Accounts.AccountName, Accounts.Ask, Warnings.Direction, Warnings.Rate, Warnings.Active
FROM Warnings INNER JOIN
Subscriptions ON Warnings.SubscriptionID = Subscriptions.SubscriptionID INNER JOIN
Accounts ON Subscriptions.AccountID = Accounts.AccountID AND
CASE
WHEN Warnings.Direction=0 THEN Accounts.Ask < Warnings.Rate
WHEN Warnings.Direction=1 THEN Accounts.Ask > Warnings.Rate
END
WHERE (Warnings.Active = 1)
This doesn't work, but could it, or am I barking up the wrong tree?
Not sure I'm expressing myself understandably here, but the point is to return all true Warnings, regardless of whether it's '1.0828 < 1.0900' or '1.0828 > 1.0800' as both are true at the same time. Any way to fix this?
TIA!
Dennis

Answer 1

I think this is what you're looking for...
SELECT
w.WarningID,
s.UserID,
a.AccountName,
a.Ask,
w.Direction,
w.Rate,
w.Active
FROM
Warnings w
INNER JOIN Subscriptions s
ON w.SubscriptionID = s.SubscriptionID
INNER JOIN Accounts a
ON s.AccountID = a.AccountID
WHERE
w.Active = 1
AND 1 = CASE
WHEN w.Direction = 1 AND a.Ask > w.Rate THEN 1
WHEN w.Direction = 0 AND a.Ask < w.Rate THEN 1
ELSE 0
END
HTH,
Jason
Jason Long