Question

Given a table with a single money column how do I calculate the smallest difference between any two values in that table using TSQL? I’m looking for the performance optimized solution, which will work with millions of rows.

Answer 1

For SQL Server 2012 you could use

;WITH CTE
     AS (SELECT YourColumn - Lag(YourColumn) OVER (ORDER BY YourColumn) AS Diff
         FROM   YourTable)
SELECT 
      Min(Diff) AS MinDiff
FROM   CTE 

This does it with one scan of the table (ideally you would have an index on YourColumn to avoid a sort and a narrow index on that single column would reduce IO).

I can’t think of a nice way of getting it to short circuit and so do less than one scan of the table if it finds the minimum possible difference of zero. Adding MIN(CASE WHEN Diff = 0 THEN 1/0 END) to the SELECT list and trapping the divide by zero error as a signal that zero was found would probably work but I can’t really recommend that approach…