Best way to write SQL delete statement, deleting pairs of records

johanpm :

I have a MySQL database with just 1 table: Fields are: blocknr (not unique), btcaddress (not unique), txid (not unique), vin, vinvoutnr, netvalue.

Indexes exist on both btcaddress and txid.

Data in it looks like this:

I need to delete all "deletable" record pairs. An example is given in red. Conditions are:

txid must be the same (there can be more than 2 records with same txid)
vinvoutnr must be the same
vin must be different (can have only 2 values 0 and 1, so 1 must be 0 other must be 1)

In a table of 36M records, about 33M records will be deleted.

I've used this:

delete t1 
from registration t1 
inner join registration t2 
where t1.txid=t2.txid and t1.vinvoutnr=t2.vinvoutnr and t1.vin<>t2.vin;

It works but takes 5 hours.

Maybe this would work too (not tested yet):

delete t1 
from registration as t1, registration as t2 
where t1.txid=t2.txid and t1.vinvoutnr=t2.vinvoutnr and t1.vin<>t2.vin;

Or do I forget about a delete query and try to make a new table with all non-delatables in and then drop the original ?

Database can be offline for this delete query.

Gordon Linoff :

Based on your question, you are deleting most of the rows in the table. That is just really expensive. A better approach is to empty the table and re-populate it:

create table temp_registration as
    <query for the rows to keep here>;

truncate table registration;

insert into registration
    select *
    from temp_registration;

Your logic is a bit hard to follow, but I think the logic on the rows to keep is:

select r.*
from registration r
where not exists (select 1
                  from registration r2
                  where r2.txid = r.txid and
                        r2.vinvoutnr = r.vinvoutnr and
                        r2.vin <> r.vin
                 );

For best performance, you want an index on registration(txid, vinvoutnr, vin).