update receive_message a, receive_message b
set a.customer=b.fromUserName
where a.msgId = b.msgId
oracle中实现
update MULTIMESSAGE b set b.sessionId=(select a.sender from MULTIMESSAGE a where a.id=b.id)
where b.id in(select b.id from MULTIMESSAGE b, MULTIMESSAGE a where b.id=a.id);