Query running slow after adding criteria - sql

Question

With much help from others I have this sql statement that calculates the difference in mileage (+ or -) between records in my table. Problem is that when I add a criteria (>0) to the the calculated value it dramatically slows my query. If I add a criteria to any other field then things run as expected (no long delay).
SELECT T1.Date,
T1.Route,
T1.BookingID,
T1.StreetNumber,
T1.Street,
T1.Arrive,
T1.Perform,
T1.Miles,
T1.Miles - (SELECT Miles
FROM Test1 AS T2
WHERE T2.Route = T1.Route
AND T2.IDNumber = (SELECT Min(IDNumber)
FROM Test1 AS T3
WHERE T3.Route = T1.Route
AND T3.IDNumber >
T1.IDNumber)) AS
Difference
FROM Test1 AS T1
GROUP BY T1.Date,
T1.Route,
T1.BookingID,
T1.StreetNumber,
T1.Street,
T1.Arrive,
T1.Perform,
T1.Miles,
T1.IdNumber,
T1.Status,
T1.Activityy
HAVING (( ( [T1].[Miles] - (SELECT Miles
FROM Test1 AS T2
WHERE T2.Route = T1.Route
AND T2.IDNumber = (SELECT Min(IDNumber)
FROM Test1 AS T3
WHERE T3.Route = T1.Route
AND T3.IDNumber >
T1.IDNumber)) ) > 0 ))
ORDER BY T1.IdNumber;

Answer 1

Your difference is just finding the next record with miles.
If you database supports row_number() or lag(), then you can rewrite this query using windows functions rather than multiple self-joins. That should fix the performance problem.
Otherwise, rewrite the query so the joins are in the "from" clause. That should also fix the problem.
Finally, if you want to use a temporary table, put all the results in a temporary table and do the selection afterwards. (This is not my preferred approach, but for a one-time query it might be the fastest solution.)