Oracle 'Partition By' and 'Row_Number' keyword

Question

I have a SQL query written by someone else and I\'m trying to figure out what it does. Can someone please explain what the Partition By and Row_Number

Answer 1

I often use row_number() as a quick way to discard duplicate records from my select statements. Just add a where clause. Something like...

select a,b,rn 
  from (select a, b, row_number() over (partition by a,b order by a,b) as rn           
          from table) 
 where rn=1;