[Koha] SQL report for list of authorities with occurrences

Dear all, I have been wandering the web in the last days but couldn't find a solution to my problem : I have a SQL report to obtain a list of authorities (subject : 250a and subfields), but in order to clean the indexes I would like to create a SQL report to obtain a list of authorities with their occurences (how many times each authority has been used). Also, sorting it by alphabetical order would be great. Of course I can see them on Koha but surfing 140 pages is not ideal! We are on Koha 3.22. Does anyone have any idea how to do that? Thanks to all, Caterina