有一个表LEANR,表里有三个字段分别是学生ID(student_id),课程(kc),成绩(grade),要求用一条查询语句搜索出每一门课程的前两名。
答案:select student_id,kc,grade from (select student_id,kc,grade,number=(select count(distinct grade) from learn where t.kc=kc and t.grade<grade) from learn t ) tt where number>2