update ex_student_answer set answer = null where paper_id = #{paperId} AND student_id = #{studentId} DELETE FROM ex_student_answer WHERE paper_id = #{paperId} AND student_id = #{studentId} select count(1) from ex_student_answer where paper_id=#{paperId} and student_id=#{studentId} select count(1) from ex_student_answer a inner join ex_question b on b.id=a.question_id where a.paper_id=#{paperId} and a.student_id=#{studentId} and b.question_type=#{questionType} and a.passed=1 select * from ex_student_answer where paper_id=#{paperId} and student_id=#{studentId} and question_id=#{questionId}