例如三个表A,B,C的关联:如果B的二级数据或C的二级数据不一定存在,用以下语句:delete A,B,C from A left join B on B.id_b=A.id left join C on C.id_c=A.id where (B.id_b=A.id) or (C.id_c=A.id);删除3个表都存在的关联数据:delete A,B,C from A,B,C where A.id=B.id_b and A.id=C.id_c。