MySQL-代码-全站搜索场景-union all-order by-limit 均有意义
select id,update_time ,"course" from eduinp_user_online_course_status where container_id = 'BaoXianFuWu' union all
select id,update_time ,"exam" from eduinp_user_online_exam_status where container_id = 'BaoXianFuWu' order by id asc limit 1,9
全站搜索场景:多个表查询,order by 也是作用于对全部的数据、limit是对 union all 的结果进行处理的
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