SQL Server query to find where all preceding numbers are not included per each ID for a specific column

Question

I am having a hard time trying to explain this succinctly but basically I need to query Table A for each ID number and find where in the positions column there are missing sequential numbers for each specific ID. If there is a position 7 for a certain ID, then there should be a 6, 5, 4, 3, 2, 1 position for that ID as well. Each ID can have anywhere from 1-15 position records.

Does anyone have any suggestions on the best way to go about this?

Edited to Add: There is only one ID column, it is called GlobalID. There is only one Positions column. The end result is that I will update an Issues column with a code specific to the problem, it will populate with PositionsIncorrect for each GlobalID record where there is an incorrect sequence of numbers in the Positions column.

Answer 1

If you just want to identify the gaps, you can use lead() in a subuqery to get the value of the next position for the same id , and then do comparison in the outer query:

select * 
from (
    select
        id,
        position,
        lead(position) over(partition by id order by position) lead_position
    from tableA
) x
where lead_position is not null and lead_position != position + 1

This will return one row for each record of the same id where the next record is not in sequence, along with the position of the next record.

Answer 2

Something like this will show which positions are missing:

DECLARE @t table
(
    ID int
    , Position int
)

INSERT INTO @t (ID, Position)
VALUES
(1, 4)
, (1, 15)
, (2, 3)
, (2, 10)
;

WITH cte
AS
(
    SELECT
        ID
        , MIN(Position) Position
        , MAX(Position) MaxPosition
    FROM @t
    GROUP BY ID

    UNION ALL

    SELECT
        ID
        , Position + 1
        , MaxPosition
    FROM cte
    WHERE Position + 1 <= MaxPosition
)

SELECT
    C.ID
    , C.Position
    , CAST(CASE WHEN T.ID IS NULL THEN 1 ELSE 0 END AS bit) Missing
FROM
    cte C
    LEFT JOIN @t T ON
        C.ID = T.ID
        AND C.Position = T.Position
ORDER BY
    ID
    , Position
OPTION (MAXRECURSION 0)