limit to 1 per where or clause

I have managed to get blog posts displayed from each blog category but I want to limit it to 1 article from each blog category but unsure how to do it in the sql query I have, below is what I have so far

(SELECT BP.postID,postTitle,postSlug,postDesc,postDate,postImage
        FROM 
          blog_posts BP, blog_post_cats BPC 
    WHERE 
       BPC.catID = 6 AND BPC.postID = BP.postID OR BPC.catID = 5 AND BPC.postID = BP.postID OR BPC.catID = 4 AND BPC.postID = BP.postID OR BPC.catID = 1 AND BPC.postID = BP.postID
     )
    UNION
    (SELECT BP.postID,postTitle,postSlug,postDesc,postDate,postImage
        FROM 
          blog_posts BP, blog_post_cats BPC
    WHERE 
       BPC.catID = BPC.postID = BP.postID
     )