Append a Query

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