use xfgs;
SET SQL_SAFE_UPDATES = 0;
SET @num = 0;
update xfgs.news_t t set t.orderNum= (@num := @num + 1)

按排序后更新

use xfgs;
SET SQL_SAFE_UPDATES = 0;
SET @num = 0;
update xfgs.news_t t set t.orderNum= (@num := @num + 1) order by createtime