join条件为find_in_set要怎么写

我的sql是这样的

select g.Fid, g.Fname, g.Fstatus,g.Frules, group_concat(a.Fname) as active from t_auth_group g inner join t_auth_active a on find_in_set(a.Fid, g.Frules)

join条件是find_in_set 用构造器应该怎么写？