SQL - Find missing int values in mostly ordered sequential series

Question

I manage a message based system in which a sequence of unique integer ids will be entirely represented at the end of the day, though they will not necessarily arrive in orde

Answer 1

I've been there.

FOR ORACLE:

I found this extremely useful query on the net a while ago and noted down, however I don't remember the site now, you may search for "GAP ANALYSIS" on Google.

SELECT   CASE
             WHEN ids + 1 = lead_no - 1 THEN TO_CHAR (ids +1)
          ELSE TO_CHAR (ids + 1) || '-' || TO_CHAR (lead_no - 1)
         END
             Missing_track_no
   FROM   (SELECT   ids,
                    LEAD (ids, 1, NULL)
                     OVER (ORDER BY ids ASC)
                        lead_no
             FROM   YOURTABLE
             )
   WHERE   lead_no != ids + 1

Here, the result is:

MISSING _TRACK_NO
-----------------
       6

If there were multiple gaps,say 2,6,7,9 then it would be:

MISSING _TRACK_NO
-----------------
        2
       6-7
        9