IIF Function returning incorrect calculated values - SQL Server - sql

Question

I am writing a query to show returns of placing each way bets on horse races
There is an issue with the PlaceProfit result - This should show a return if the horses finishing position is between 1-4 and a loss if the position is => 5
It does show the correct return if the horses finishing position is below 9th, but 10th place and above is being counted as a win.
I include my code below along with the output.
ALTER VIEW EachWayBetting
AS
SELECT a.ID,
RaceDate,
runners,
track.NAME AS Track,
horse.NAME as HorseName,
IndustrySP,
Place AS 'FinishingPosition',
-- // calculates returns on the win & place parts of an each way bet with 1/5 place terms //
IIF(A.Place = '1', 1.0 * (A.IndustrySP-1), '-1') AS WinProfit,
IIF(A.Place <='4', 1.0 * (A.IndustrySP-1)/5, '-1') AS PlaceProfit
FROM dbo.NewRaceResult a
LEFT OUTER JOIN track ON track.ID = A.TrackID
LEFT OUTER JOIN horse ON horse.ID = A.HorseID
WHERE a.Runners > 22
This returns:

Answer 1

As I mention in the comments, the problem is your choice of data type for place, it's varchar. The ordering for a string data type is completely different to that of a numerical data type. Strings are sorted by character from left to right, in the order the characters are ordered in the collation you are using. Numerical data types, however, are ordered from the lowest to highest.
This means that, for a numerical data type, the value 2 has a lower value than 10, however, for a varchar the value '2' has a higher value than '10'. For the varchar that's because the ordering is completed on the first character first. '2' has a higher value than '1' and so '2' has a higher value than '10'.
The solution here is simple, fix your design; store numerical data in a numerical data type (int seems appropriate here). You're also breaking Normal Form rules, as you're storing other data in the column; mainly the reason a horse failed to be classified. Such data isn't a "Place" but information on why the horse didn't place, and so should be in a separate column.
You can therefore fix this by firstly adding a new column, then updating it's value to be the values that aren't numerical and making place only contain numerical data, and then finally altering your place column.
ALTER TABLE dbo.YourTable ADD UnClassifiedReason varchar(5) NULL; --Obviously use an appropriate length.
GO
UPDATE dbo.YourTable
SET Place = TRY_CONVERT(int,Place),
UnClassifiedReason = CASE WHEN TRY_CONVERT(int,Place) IS NULL THEN Place END;
GO
ALTER TABLE dbo.YourTable ALTER COLUMN Place int NULL;
GO
If Place does not allow NULL values, you will need to ALTER the column first to allow them.

Answer 2

In addition to fixing the data as Larnu suggests, you should also fix the query:
SELECT nrr.ID, nrr.RaceDate, nrr.runners,
t.NAME AS Track, t.NAME as HorseName, nrr.IndustrySP,
Place AS FinishingPosition,
-- // calculates returns on the win & place parts of an each way bet with 1/5 place terms //
(CASE WHEN nrr.Place = 1 THEN (nrr..IndustrySP - 1.0) ELSE -1 END) AS WinProfit,
(CASE WHEN nrr.Place <= 4 THEN (nrr.IndustrySP - 1.0) / 5 THEN -1 END) AS PlaceProfit
FROM dbo.NewRaceResult nrr LEFT JOIN
track t
ON t.ID = nrr.TrackID LEFT JOIN
horse h
ON h.ID = nrr.HorseID
WHERE nrr.Runners > 22;
The important changes are removing single quotes from numbers and column names. It seems you need to understand the differences among strings, numbers, and identifiers.
Other changes are:
Meaningful table aliases, rather than meaningless letters such as a.
Qualifying all column references, so it is clear where columns are coming from.
Switching from IFF() to CASE. IFF() is bespoke SQL Server; CASE is standard SQL for conditional expressions (both work fine).
Being sure that the types returned by all branches of the conditional expressions are consistent.
Note: This version will work even if you don't change the type of Place. The strings will be converted to numbers in the appropriate places. I don't advocate relying on such silent conversion, so I recommend fixing the data.
If place can have non-numeric values, then you need to convert them:
(CASE WHEN TRY_CONVERT(int, nrr.Place) = 1 THEN (nrr..IndustrySP - 1.0) ELSE -1 END) AS WinProfit,
(CASE WHEN TRY_CONVERT(int, nrr.Place) <= 4 THEN (nrr.IndustrySP - 1.0) / 5 THEN -1 END) AS PlaceProfit
But the important point is to fix the data.