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

You didn't state your DBMS, so I'm assuming PostgreSQL:

select aid as missing_id
from generate_series( (select min(id) from message), (select max(id) from message)) as aid
  left join message m on m.id = aid
where m.id is null;  

This will report any missing value in a sequence between the minimum and maximum id in your table (including gaps that are bigger than one)

psql (9.1.1)
Type "help" for help.

postgres=> select * from message;
 id
----
  1
  2
  3
  4
  5
  7
  8
  9
 11
 14
(10 rows)


postgres=> select aid as missing_id
postgres-> from generate_series( (select min(id) from message), (select max(id) from message)) as aid
postgres->   left join message m on m.id = aid
postgres-> where m.id is null;
 missing_id
------------
          6
         10
         12
         13
(4 rows)
postgres=>