在update 中的 where 子句中使用子查询：

UPDATE mg_page_log as a  SET  page_num=1 WHERE id in( SELECT id  from mg_page_log WHERE id < 100 GROUP BY visit_id)

会报：

You can't specify target table 'a' for update in FROM clause 错误

所以正确的是：

UPDATE mg_page_log as a ,( SELECT id  from mg_page_log WHERE id < 100 GROUP BY visit_id)as b SET  page_num=1 WHERE a.id = b.id

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UPDATE customer as a ,customer0 as aa SET a.lastVisitTime = aa.lastFollowTime ,a.visitCount = 1 WHERE a.id = aa.id AND a.phase=2 AND a.lastVisitTime = 0