select a_id as id,
s_question as question,
s_answer as answer
from t_subjective
union
select sa_id as id,
sa_question as question,
sa_answer as answer
from t_saccessory
或者还可以
select id,question,answer
from(
select a_id as id,
s_question as question,
s_answer as answer
from t_subjective
union
select sa_id as id,
sa_question as question,
sa_answer as answer
from t_saccessory) ttt