结合连表…两条语句的效率相差甚大！主要是OR与IN的区别……

SELECT tid,sum(downloads) AS downloads FROM cdb_attachments GROUP BY tid ORDER BY aid

UPDATE cdb_threads SET downs = '$downloads' WHERE tid = '$tid'

SELECT t.tid, t.views, t.subject, sum( a.downloads ) AS downloads
FROM cdb_threads t
LEFT JOIN cdb_attachments a ON t.tid = a.tid
WHERE t.fid
IN (
'62', '61', '60', '59', '58', '57', '56', '55', '31', '30', '29', '28', '27', '26', '25', '24', '19'
)
GROUP BY t.tid
ORDER BY downloads DESC
LIMIT 6


SELECT tid,sum(downloads) AS downloads FROM cdb_attachments GROUP BY tid ORDER BY aid

UPDATE cdb_threads SET downs = '$downloads' WHERE tid = '$tid'

SELECT t.tid, t.views, t.subject, sum( a.downloads ) AS downloads
FROM cdb_threads t
LEFT JOIN cdb_attachments a ON t.tid = a.tid
WHERE (
t.fid = '62' OR t.fid = '61' OR t.fid = '60' OR t.fid = '59' OR t.fid = '58' OR t.fid = '57' OR t.fid = '56' OR t.fid = '55' OR t.fid = '31' OR t.fid = '30', '29' OR t.fid = '28' OR t.fid = '27' OR t.fid = '26' OR t.fid = '25' OR t.fid = '24' OR t.fid ='19'
)
GROUP BY t.tid
ORDER BY downloads DESC
LIMIT 6

昨天匆匆的发帖！忘了说是用discuz论坛的数据表，数据记录是主题表3W，附件表是5w条记录以上，同时还考虑一个sum求和的区别==

运行速度相差几百倍……哈哈！