大致如下，就是把in改为left join：

SELECT b.BCLID AS BCLID, b.PcbID AS PcbID, b.PN AS PN, b.CompName AS CompName
FROM ( SELECT CompName FROM BomCompListInfo
WHERE PcbID = 80
GROUP BY CompName
HAVING count(*) > 1 ) c
left join BomCompListInfo b on b.CompName=c.CompName
left join BomInfo a on a.PN = b.PN AND a.PcbID = b.PcbID
WHERE a.PcbID = 80
ORDER BY b.CompName