Automate running SQL filetype scripts when opening a PHP file

Question

When I open a PHP file in Vim I want Vim to provide SQL assistance as well as all the PHP assistance.
From :h sql-completion-filetypes:

This can be enabled easily with the following steps (assuming a Perl file):

1.  :e test.pl  
2.  :set filetype=sql  
3.  :set ft=perl

I would like to automate this: So far I have tried

Appending the following commands to ~/.vim/after/ftplugins/php.vim

:set filetype=sql  
:set ft=php

This throws errors like

Error detected while processing FileType Auto commands for "*":       
E218: autocommand nesting too deep

Which I'm assuming is happening because when whenever the set ft=php command is run - it then re-triggers the ~/.vim/after/ftplugins/php.vim script which then re-triggers the set ft=php statement.
Is it possible to automate running these commands :set filetype=sql, :set ft=php when opening a php file?

Answer 1

On my Vim (7.4.944), the SQL filetype plugin performs the following check:

if !exists("*SQL_SetType")
    " NOTE: You cannot use function! since this file can be
    " sourced from within this function.  That will result in
    " an error reported by Vim.

That seems to be a good way to load sql.vim once. So, in my ~/.vim/ftplugin/php.vim, I added:

if !exists("*SQL_SetType")
    set ft=sql
    set ft=php
endif

I don't use SQL in PHP, but AFAICT, the SQL settings were loaded.