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2207/MySQL练习题/查询练习.md

@@ -495,25 +495,93 @@ LEFT JOIN courses c ON c.id = sc.course_id
 WHERE sc.score > 80 AND c.id = '01';
 
 #32.求每门课程的学生人数
-
+SELECT c.`name`, COUNT(*)
-
+FROM scores s, courses c
+WHERE s.course_id = c.id
+GROUP BY c.id;
 #33.成绩不重复，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩
+SELECT st.`name`, sc.score
+FROM students st, scores sc, courses c, teachers t
+WHERE st.id =  sc.student_id AND sc.course_id = c.id 
+AND c.teacher_id = t.id AND t.`name` = '张三'
+ORDER BY sc.score DESC 
+LIMIT 1;
 
 #34.成绩有重复的情况下，查询选修「张三」老师所授课程的学生中，成绩最高的学生信息及其成绩
-
+SELECT st.`name`, sc.score
+FROM students st, scores sc
+WHERE st.id =  sc.student_id AND sc.score = (
+	SELECT MAX(score)
+	FROM scores, courses, teachers
+	WHERE scores.course_id = courses.id 
+	AND courses.teacher_id = teachers.id AND teachers.`name` = '张三'
+);
 #35.查询不同课程成绩相同的学生的学生编号、课程编号、学生成绩
+SELECT st.id, sc1.course_id, sc1.score
+FROM students st, scores sc1
+WHERE st.id = sc1.student_id AND sc1.score = ANY(
+	SELECT sc2.score
+	FROM scores sc2
+	WHERE sc2.student_id = st.id AND sc2.course_id != sc1.course_id
+);
 
 #36.查询每门课成绩最好的前两名
-
+SELECT c1.`name`, c1.score
+FROM (
+	SELECT c.`name`, sc.score
+	FROM scores sc, courses c
+	WHERE sc.course_id = c.id AND c.id = '01'
+	ORDER BY sc.score DESC
+	LIMIT 2
+)c1
+UNION ALL
+SELECT c2.`name`, c2.score
+FROM (
+	SELECT c.`name`, sc.score
+	FROM scores sc, courses c
+	WHERE sc.course_id = c.id AND c.id = '02'
+	ORDER BY sc.score DESC
+	LIMIT 2
+)c2
+UNION ALL
+SELECT c3.`name`, c3.score
+FROM (
+	SELECT c.`name`, sc.score
+	FROM scores sc, courses c
+	WHERE sc.course_id = c.id AND c.id = '03'
+	ORDER BY sc.score DESC
+	LIMIT 2
+)c3;
 #37.统计每门课程的学生选修人数（超过 5 人的课程才统计）
+SELECT c.`name`, COUNT(*) c
+FROM scores s, courses c
+WHERE s.course_id = c.id
+GROUP BY c.id
+HAVING c>5;
 
 #38.检索至少选修两门课程的学生学号
-
+SELECT st.id, st.`name`
+FROM students st
+WHERE (
+	SELECT COUNT(*)
+	FROM scores sc
+	WHERE sc.student_id = st.id
+)>=2;
 #39.查询选修了全部课程的学生信息
+SELECT st.*
+FROM students st, scores sc
+WHERE st.id = sc.student_id
+GROUP BY st.id
+HAVING COUNT(*) = 3;
 
 #40.查询各学生的年龄，只按年份来算
+SELECT s.`name`, TIMESTAMPDIFF(YEAR,s.birth,NOW()) 
+FROM students s;
 
 #41.查询各学生的年龄，按照出生日期来算，当前月日 < 出生年月的月日则，年龄减一
+SELECT s.`name`, IF(DATE_FORMAT(s.birth,'%m-%d') < DATE_FORMAT(NOW(),'%m-%d'), 
+TIMESTAMPDIFF(YEAR,s.birth,NOW())-1, TIMESTAMPDIFF(YEAR,s.birth,NOW()))
+FROM students s;
 
 #42.查询本周过生日的学生