I wrote a script that created new Opportunities, but I set the timing wrong and it ran every hour instead of once a day. This created a bit of a mess... here's how I cleaned it up.

Opportunities DuDup

-- setup temp table
create table `opp_dups` (
    `id` varchar(36) NOT NULL,
    PRIMARY KEY (`id`)
);

-- copy the dup IDs into the temp table...
insert into opp_dups(id)
select distinct(opp1.id) from opportunities opp1
    join opportunities opp2 on opp1.name=opp2.name and opp1.id <> opp2.id
    and opp1.date_closed = opp2.date_closed
    and opp1.deleted = 0 and opp2.deleted = 0
    and length(opp1.id) = 36 and length(opp2.id) = 36;

-- group the dupes
select id,name,date_closed,count(*) as dups from opportunities
where opportunities.deleted = 0
and length(id) = 36
group by name,date_closed
order by name asc;

-- the wrapup, showing dupe groups that actually count > 1
select * from
(
    select id,name,date_closed,count(*) as dups from opportunities
    where opportunities.deleted = 0
    and length(id) = 36
    group by name,date_closed
    order by name asc
) as sub
where sub.dups > 1;


-- the re-wrapped update sets deleted=2, which means 'save me!'
update opportunities set deleted=2 where id in
(
    select * from
    (
        select id as dups from opportunities
        where opportunities.deleted = 0
        and length(id) = 36
        group by name,date_closed
        order by name asc
    ) as sub
    where sub.dups > 1
);

-- the re-wrapped update that actually soft-deletes things...
update opportunities 
set deleted=1 where deleted=0 and id in 
(
    select id from opp_dups
);

-- and re-activate the '2' group
update opportunities set deleted=0 where deleted=2;
 
-- and see what we have now
select id,name,date_closed from opportunities where deleted = 0 and length(id) = 36;
 
-- drop that temp table
drop table `opp_dups`;