Hello Timur,
Thanks for the patches! The :delete-from one is perfect. The sql-error one is a good idea, but your patch is completely broken (you can't do (error 'sql-error "~a" val)). I've committed something similar to the repository. (Also, submitting patches created by 'darcs send -o patchfilename' makes it easier for me to merge them.)
Cheers, Marijn