MySQL Query Error: Unknown column 'cmcka' in 'where clause'

Query: select a.intMediaID, a.strMediaTitle, a.strAuthor, x.strLinkText from Xref x, MediaLibrary a WHERE a.bitPublish = 1 AND x.intPrimaryID = cmcka AND x.intLinkID = a.intMediaID AND x.intTypeID = 28 AND a.dtmPubDate <= CURDATE() AND (a.dtmExpDate >= CURDATE() OR a.dtmExpDate IS NULL) ORDER BY x.intSortOrder, a.strMediaTitle