SELECT A.FNAME || ' ' || A.LNAME "Author", count(A.AUTHORID) FROM BOOKAUTHOR BA JOIN AUTHOR A ON BA.AUTHORID = A.AUTHORID GROUP BY A.FNAME || ' ' || A.LNAME SQL 小提琴演示 回答by WW. 你失败的陈述是这样的: USING(AUTHOR.AUTHORID) 但您只能拥有: USING(AUTHORID) 尝试...