-- 2、查询“01“课程比“02“课程成绩低的学生的信息及课程分数

SELECT st.*, sc.s_score AS '语文', sc2.s_score AS '数学' FROM student st LEFT JOIN score sc ON sc.s_id=st.s_id AND sc.c_id='01' LEFT JOIN score sc2 ON sc2.s_id=st.s_id AND sc2.c_id='02' WHERE sc.s_score < sc2.s_score