Question

I have this table

ID  |  Seq  
------------
 A      1      
 A      2      
 A      3      
 B      1      
 B      2     
 B      3     
 B      3     <--duplicate seq where ID=B
 C      1     
 C      2
 C      4     <--missing seq id number 3
 D      1
 D      2
 .      .
 .      .

Is there a way to detect if/when there is an error in the logic of the Seq column, specifically if there are jumps and/or duplicates.

Answer 1

try this:

this should work both in sql server as well as Oracle

select ID,seq
       from(
            select ID,seq,
                   row_number() over (partition by id order by seq ) rn
            from t_seq)a
where a.seq<>a.rn

SQL fiddle demo for SQL server

SQL Fiddle demo for Oracle