runtime(sql): set commentstring for sql files in ftplugin

closes: #14800

Signed-off-by: Riley Bruins <ribru17@hotmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/ftplugin/sql.vim

@@ -4,6 +4,7 @@
 " Maintainer:  David Fishburn <dfishburn dot vim at gmail dot com>
 " Last Change: 2017 Mar 07
 "              2024 Jan 14 by Vim Project (browsefilter)
+"              2024 May 18 by Vim Project (set comment options)
 " Download:    http://vim.sourceforge.net/script.php?script_id=454
 
 " For more details please use:
@@ -105,6 +106,8 @@ set cpo&vim
 setlocal formatoptions-=t
 setlocal formatoptions+=c
 
+setlocal comments=:-- commentstring=--\ %s
+
 " Functions/Commands to allow the user to change SQL syntax dialects
 " through the use of :SQLSetType <tab> for completion.
 " This works with both Vim 6 and 7.
@@ -266,7 +269,7 @@ if exists("b:did_ftplugin") && exists("b:current_ftplugin") && b:current_ftplugi
     finish
 endif
 
-let b:undo_ftplugin = "setl comments< formatoptions< define< omnifunc<" .
+let b:undo_ftplugin = "setl comments< commentstring< formatoptions< define< omnifunc<" .
             \ " | unlet! b:browsefilter b:match_words"
 
 " Don't load another plugin for this buffer