Problem with SQL query (eats swap)

Hi, I have two tables into which I dump mail statistics.  The two tables are:

create table attachments ( id text, attachment text
);
create table mail ( id text, size int, whofrom text, subject text, date datetime, inout char
);

The table mail holds information about each mail message.  The table attachments holds the name of any attachments.
Linkingthe attachment(s) and the message is the id.
 

I want to delete all records relating to mail that is over two months old.  I tried:

select count(*) from attachments a where a.id in (select m.id from mail m where m.date < now()-62);

but ran out of swap.  The mail table is 19Mb, the attachment one 1Mb.  I was up to 380Mb of swap used on a machine with
128MbRAM, and over 15 minutes run time.  At that point I killed the query.
 

I next tried is as follows:

drop table temp;
select id into temp from mail where date < now()-62;
delete from attachments where id in (select id from temp);
delete from mail where date < now()-62;

This worked fine and deleted the records as intended in a few minutes.  Can anyone see why the initial query ate so
muchswap?
 


Cheers
Kevin
kevin@sartorelli.gen.nz