Remove all files except for last file of each month

With the file zz containing the list of file names, this works, so just replace cat zz.

cat zz | grep -vF -f <(cat zz|sort -r|uniq -w11)

e.g. echo *.sql | grep -vF -f <( echo *.sql | sort -r | uniq -w11 ) | xargs rm

As is, it won't work if spaces in file names, and very fragile to filename length.