Delete duplicate rows from Oracle tables

delete from $table_name where rowid in
  (
  select "rowid" from
     (select "rowid", rank_n from
         (select rank() over (partition by $primary_key order by rowid) rank_n, rowid as "rowid"
             from $table_name
             where $primary_key in
                (select $primary_key from $table_name
                  group by $all_columns
                  having count(*) > 1
                )
             )
         )
     where rank_n > 1
  )

One of the most important features of Oracle is the ability to detect and remove duplicate rows from a table. While many Oracle DBA place primary key referential integrity constraints on a table, many shops do not use RI because they need the flexibility.

Use self-join to delete duplicate rows

The most effective way to detect duplicate rows is to join the table against itself as shown below.

select
   book_unique_id,
   page_seq_nbr,
   image_key
from
   page_image a
where
   rowid >
     (select min(rowid) from page_image b
      where
         b.key1 = a.key1
      and
         b.key2 = a.key2
      and
         b.key3 = a.key3
      );

Please note that you must specify all of the columns that make the row a duplicate in the SQL where clause. Once you have detected the duplicate rows, you may modify the SQL statement to remove the duplicates as shown below:

delete from
   table_name a
where
   a.rowid >
   any (select b.rowid
   from
      table_name b
   where
      a.col1 = b.col1
   and
      a.col2 = b.col2
   )
;

Use analytics to delete duplicate rows

You can also detect and delete duplicate rows using Oracle analytic functions:

delete from
   customer
where rowid in
 (select rowid from
   (select
     rowid,
     row_number()
    over
     (partition by custnbr order by custnbr) dup
    from customer)
  where dup > 1);

As we see, there are several ways to detect and delete duplicate rows from Oracle tables

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Reader Comments:

Removing duplicate table rows where rows have NULL values

Rob Arden states:  The tip on this page helped with removing duplicate rows from Oracle tables. I thought this might be useful so I'm passing it on: I needed to add a null check because this fails to remove dupe rows where the fields match on a null value.  So instead of the given:

delete from
   table_name a
where
   a.rowid >
   any (select b.rowid
   from
      table_name b
   where
      a.col1 = b.col1
   and
      a.col2 = b.col2
   )
;

I needed to do the following to remove all of the duplicate table rows:

delete from
   table_name a
where
   a.rowid >
   any (select b.rowid
   from
      table_name b
   where
      (a.col1 = b.col1 or (a.col1 is null and b.col1 is null))
   and
      (a.col2 = b.col2 or (a.col2 is null and b.col2 is null))
   )
;

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