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/*
表A 是贴子内容表
A
topicID title postDate ,lastReplyDate
表B是保存回贴的结果如下
TopicID ReplyText,ReplyDate \
问题:现在A表的最后回复时间(LasyReplyDate) 是段出错了,要用B表来修改A表的lastReplyDate
即要 求出B表中 最近max(ReplyDate) 回复时间 修表A
*/
update A set lastReplyDate=b.ReplyDate
(select TopicID,max(ReplyDate) ReplyDate from b group by TopicID) b where A.TopicID=B.TopicID
UPDATE TA SET lastReplyDate=B.ReplyDate FROM (SELECT TopicID,MAX(ReplyDate)ReplyDate FROM TB GROUP BY TOPICID)B
WHERE TA.TOPICID=B.TOPICID
UPDATE A
SET lastReplyDate =C.ReplyDate
FROM A
LEFT JOIN
(
SELECT TopicID,MAX(ReplyDate ) ReplyDate
FROM B
GROUP BY TopicID
)C ON C.TopicID=A.TopicID
UPDATE a SET a.lastReplyDate = md
FROM tableA a
INNER JOIN
(
SELECT topicid,MAX(ReplyDate) md FROM tableB GROUP BY topicid
) b
ON a.topicid=b.topicid