delete b.*
from tbl a
inner join tbl b
on a.col1 = b.col1
[download]

This looks like a self-join of the table with itself to me. But if your posted SQL was just sample code, maybe you should work more on workable samples you post. If not, consider thinking more about what you really want to do.

One standard practice I have when using rm or delete is to run ls respectively select first, and look at the output, and think long and hard about whether the output I see is the stuff I want deleted. Only then I change the select into a delete.

I'd guess that the rows you have left contain a null in that column, since null doesn't equal null (in the databases I use).

...roboticus