表间查询

select positionChild,(select Remark from Freqs a join Contents b on a.ID=b.senior where b.ID=c.id) as senior,
  (select Remark from Freqs a join Contents b on a.ID=b.middle where b.ID=c.id ) as middle,
  (select Remark from Freqs a join Contents b on a.ID=b.general where b.ID=c.id ) as general
    from Contents c