一个SQL update语句

需要每隔一段时间选取最老的商户更新时间戳: 

update DP_Shop set DP_Shop.LastDate = now() where DP_Shop.ShopId in (select ShopId from DP_Shop order by LastDate limit 5); 

ERROR 1235 (42000): This version of MySQL doesn‘t yet support ‘LIMIT & IN/ALL/ANY/SOME subquery‘

多加一层: 

update DP_Shop set DP_Shop.LastDate = now() where DP_Shop.ShopId in (select t.ShopId from (select ShopId from DP_Shop order by LastDate limit 5) as t); 

可以work,但不高效，考虑下怎么优化。

最后是用临时表:

start transaction;

create temporary table tmp1986 (select ShopId from DP_Shop order by LastDate limit 1000);

update DP_Shop inner join tmp1986 on DP_Shop.ShopId = tmp1986.ShopId set LastDate = now();

DROP TABLE tmp1986; 

commit;

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