Question

This is a simpler version of the query I have.

Alias1 as 
(select distinct ID, file_tag, status, creation_date from tables where creation_dt >= sysdate and creation_dt <= sysdate + 1),

Alias2 as 
(select distinct ID, file_tag, status, creation_date from same tables creation_dt >= sysdate and creation_dt <= sysdate + 1)

select distinct Alias1.ID ID_1,
           Alias2.ID ID_2,
           Alias1.file_tag,
           Alias1.creation_date in_dt1,
           Alias2.creation_date in_dt2
    from   Alias1, Alias2
    where Alias1.file_tag = Alias2.file_tag
          and Alias1.ID != Alias2.ID
    order by Alias1.creation_dt desc

This is an example of the results. Both of these are the same, though their values are flipped.

    ID_1 ID_2  File_Tag     in_dt1          in_dt2
    70   66    Apples       6/25/2012 3:06  6/25/2012 2:53:47 PM
    66   70    Apples       6/25/2012 2:53  6/25/2012 3:06:18 PM

The goal of the query is to find more than one ID with a matching file tag and do stuff to the one submitted earlier in the day (the query runs daily and only needs duplicates from that given day). I am still relatively new to SQL/Oracle and wonder if there’s a better way to approach this problem.

Answer 1

Here is an easy way, just by chaning your comparison operation:

select distinct Alias1.ID ID_1, Alias2.ID ID_2, Alias1.file_tag,
       Alias1.creation_date in_dt1, Alias2.creation_date in_dt2
from Alias1 join
     Alias2
     on Alias1.file_tag = Alias2.file_tag and
        Alias1.ID < Alias2.ID
order by Alias1.creation_dt desc 

Replacing the not-equals with less-than orders the two ideas so the smaller one is always first. This will eliminate the duplicates. Note: I also fixed the join syntax.