[SDF]

אולי משהו כזה:

SELECT * 
FROM `sectionarticles` as t1, `sectionarticles` as t2 
WHERE t2.ArticleID = t1.ArticleID AND 
( t1.SectionID = 3 AND t2.SectionID = 4 ) OR 
( t1.SectionID = 4 AND t2.SectionID = 3);