ErcanOPAK.com

Let’s say we have this values in the database:

num
---
 1
 2
 4
 5
 6
 8
 9
 11

To Find the first missing value, we can use this:

;WITH CteRN AS(
    SELECT *,
        RN = num - ROW_NUMBER() OVER(ORDER BY num)
    FROM tbl
)
SELECT TOP 1 num - RN
FROM CteRN
WHERE RN > 0
ORDER BY num ASC