Re: Removing duplicates

[Giuseppe Broccolo <giuseppe.broccolo@xxxxxxxxxxxxxx>]

Dear Johann,

I tried (with PostgreSQL 9.2) to run the two DELETE statements you describe in your mail (the first based on the "id" field, the second on the ctid) and they work! I have to point out that if you use the DELETE based on the "id" field YOU'LL DELETE ALL RECORDS having at least one duplicate.
The "q1.id != q.id" doesn't work because query doesn't know yet its result so every row with a duplicate will match without exception.
If you use the DELETE based on ctid order you delete only records with the same "rart_id", keeping the record with the lowest "id".

Remember that if you run the first DELETE query you remove more data than you expect.

Regards,

Giuseppe.

Il 10/07/2013 09:11, Johann Spies ha scritto:

I have used this method successfully on another table but this one is not
working.

I have a table of nearly 800 million records with some duplicates in.

Here is an example:

select rart_id, r9, ra, ry, rw, rv, rp, rs, ri
from isi.rcited_ref
where rart_id = 'A1986D733500019';

renders a result of 72 records. When I do

select count(id), rart_id, r9, ra, ry, rw, rv, rp, rs, ri
from isi.rcited_ref
where rart_id = 'A1986D733500019'
group by rart_id, r9, ra, ry, rw, rv, rp, rs, ri;

It shows that there are 36 duplicates with this rart_id.

So as a test I did the following (the id-field is the primary key):

DELETE FROM isi.rcited_ref q
WHERE EXISTS(SELECT 1 FROM   isi.rcited_ref q1
   WHERE  q1.id != q.id
   AND    q.rart_id = q1.rart_id
   AND    q.r9 = q1.r9
   AND    q.ra = q1.ra
   AND    q.ry = q1.ry
   AND    q.rw = q1.rw
   AND    q.rv = q1.rv
   AND    q.rp = q1.rp
   AND    q.rs = q1.rs
   AND    q.rart_id = 'A1986D733500019'
    );

But that deletes none.  And I cannot see what went wrong.

I have also tried the same query with ctid without success:

DELETE FROM isi.rcited_ref q
WHERE EXISTS(SELECT 1 FROM   isi.rcited_ref q1
   WHERE  q1.ctid < q.ctid
   AND    q.rart_id = q1.rart_id
   AND    q.r9 = q1.r9
   AND    q.ra = q1.ra
   AND    q.ry = q1.ry
   AND    q.rw = q1.rw
   AND    q.rv = q1.rv
   AND    q.rp = q1.rp
   AND    q.rs = q1.rs
   AND    q.rart_id = 'A1986D733500019'
    );


The size of the table makes it difficult to use a 'group by'  method to
delete all duplcates.

What am I doing wrong?

Regards
Johann
-- 
Because experiencing your loyal love is better than life itself,
my lips will praise you.  (Psalm 63:3)