Can a Query fill the system?

[pam@xxxxxxxxxxxxx]

I'm running a Model 720 with 400 GB, which is usually about 75% full. Last
night, it suddenly went to 90%. When I dialled in to check it, the only
suspicious job I could find was a query that had been running for over three
hours and still hadn't created output. So I killed it, and like magic, I was
back at 75%.

Now that I've had a chance to look at yesterday's performance graphs, I find
that three times, this query and similar ones filled the disk to the
threshhold in the course of two hours. These queries link four files, one of
which is huge. Clearly, there's something wrong with the joins. I've seen this
sort of thing cause queries to run for ages to no effect, but I've never seen
them chew up disk space like that.

What could it be doing that would fill 60GB in 2 hours?

Pam Phillips