Here is an example of preventing caching of a file using .htaccess
<FilesMatch "dontcache\\.txt$">
Header unset ETag
Header set Cache-Control "max-age=0, no-cache, no-store, must-revalidate"
Header set Pragma "no-cache"
Header set Expires "Wed, 1 Jan 2000 00:00:00 UTC"
</FilesMatch>
Edit your command so it has ">/dev/null 2>&1" at the end like this:
mysql --host=localhost --user=cmh_user --database=cmh_db --password=bestpasswordever --execute="update mytable set mytable.somedata = '1' where mytable.id = '1'" >/dev/null 2>&1