how to make file extensions to syntax highlighting in vim?

Question

I have *.q files ( that are very similar to other SQL ) and I want to make vim syntax highlight it in the same way as SQL.

Answer 1

create a ~/.vim/ftdetect directory if not existing.
create a ~/.vim/ftdetect/<new-file-type-extention>.vim with content:

au BufRead,BufNewFile *.<new-file-type-extention> set filetype=<existing-file-type-extention>

Answer 2

Include it in the ~/.vim/filetype.vim, as described at Vim FAQ 26.8:

" my filetype file
if exists("did_load_filetypes")
    finish
endif
augroup filetypedetect
    au! BufRead,BufNewFile *.x       setfiletype c
augroup END

For this case it would be changed to something like this:

    au! BufRead,BufNewFile *.q       setfiletype sql

Check :help new-filetype for additional details.