It may help other beginners, so sharing..

====

SELECT @cid := c.categoryid FROM qa_categories c

WHERE c.title = 'SQL Server Interview Questions';

SELECT @nqid := IFNULL(p.postid,0) FROM qa_posts p

WHERE p.type='Q' and p.postid > 1446

AND p.categoryid = @cid

ORDER BY postid LIMIT 1;

SELECT @pqid := IFNULL(p.postid,0) FROM qa_posts p

WHERE p.type='Q' and p.postid < 1446

AND p.categoryid = @cid

ORDER BY postid DESC LIMIT 1;

SELECT @cid, @pqid, @nqid;

===========

SELECT @wid := wordid

FROM qa_words

WHERE word = 'tag1';

SELECT @nqid := IFNULL(p.postid,0) FROM qa_posts p

join qa_posttags pt

on p.postid = pt.postid

WHERE p.type='Q' and p.postid > 1446

AND pt.wordid = @wid

ORDER BY p.postid LIMIT 1;

SELECT @pqid := IFNULL(p.postid,0) FROM qa_posts p

join qa_posttags pt

on p.postid = pt.postid

WHERE p.type='Q' and p.postid < 1446

AND pt.wordid = @wid

ORDER BY p.postid DESC LIMIT 1;

SELECT @wid, @pqid, @nqid;

===========