回答:SELECT * FROM A a WHERE a.nf = '2023' AND a.bm IN (SELECT bm FROM B b WHERE b.ry = '甲' AND nf = '2023') AND ((SELECT count(1) FROM B b WHERE b.ry = '甲' AND nf = '2023') > 0)UNION allSELECT * FROM A a WHERE a.nf = '2023' AND a.bm IN (SELECT a.bm FROM A a WHERE a.nf = '2023') AND ((SELECT count(1) FROM B b WHERE b.ry = '甲' AND nf = '2023') <= 0)