– 22、查询所有课程的成绩第2名到第3名的学生信息及该课程成绩
SELECT t1.* FROM (SELECT st.*,c.c_id,c.c_name,sc.s_score FROM student st LEFT JOIN score sc ON sc.s_id=st.s_id INNER JOIN course c ON c.c_id =sc.c_id AND c.c_id="01" ORDER BY sc.s_score DESC LIMIT 1,2) t1 UNION ALL SELECT t2.* FROM (SELECT st.*,c.c_id,c.c_name,sc.s_score FROM student st LEFT JOIN score sc ON sc.s_id=st.s_id INNER JOIN course c ON c.c_id =sc.c_id AND c.c_id="02" ORDER BY sc.s_score DESC LIMIT 1,2) t2 UNION ALL SELECT t3.* FROM (SELECT st.*,c.c_id,c.c_name,sc.s_score FROM student st LEFT JOIN score sc ON sc.s_id=st.s_id INNER JOIN course c ON c.c_id =sc.c_id AND c.c_id="03" ORDER BY sc.s_score DESC LIMIT 1,2) t3
这是一道mysql难题,也是经典题,搞懂这题就懂得一类题了.
逐条解析
1.从学生表当中选择
SELECT t1.* FROM (student)
2.将学生表和分数表连接从中选择学生信息,课程id,课程名字,分数
SELECT st.*,c.c_id,c.c_name,sc.s_score FROM student st LEFT JOIN score sc ON sc.s_id=st.s_id
3.将学生表和课程表连接,倒序
,抽取第2,第3名
,且课程id为 01的课程信息
并按分数归类
INNER JOIN course c ON c.c_id =sc.c_id AND c.c_id="01" ORDER BY sc.s_score DESC LIMIT 1,2
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