Append a Query

["Alexa Kirk" <akirk@ufl.edu>]

I am trying to make a query based on the user input, for a search page.
So, I have the initial query set up like: 
$query = "select PUB_ID, AUTHOR, TITLE, YEAR  from * where
USER.USER_ID=$user and USER.USER_ID=USER_PUB.USER_ID";
 
if ($author != null){
            //append this string to the $query already stated
            " and JOURNAL_ARTICLE.AUTHOR=$author";
}
if ($title != null){
            //append this string also
            " and JOURNAL_ARTICLE.TITLE=$title";
}
 
How do you do this concatenation?
 
Thanks,
Alexa