You can't specify target table f

问题

update keywords set showcase_flag=1 where keywords.link in  (SELECT link FROM keywords where showcase_flag="是") ;

进阶

update keywords set showcase_flag=1 where keywords.link in (SELECT a.link FROM (SELECT link FROM keywords where showcase_flag="是") as a);

提高

update keywords a set a.showcase_flag = case when a.showcase_flag = '是' then '1' when a.showcase_flag = '否' then '0' end;