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smallkun 2025-02-27 10:34:54 +08:00
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2207/MySQL练习题/查询练习.md
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@ -407,16 +407,45 @@ FROM (
)s3; )s3;
#19.查询每门课程被选修的学生数 #19.查询每门课程被选修的学生数
SELECT c.`name`, COUNT(*)
FROM courses c
LEFT JOIN scores sc ON sc.course_id = c.id
GROUP BY c.id;
#20.查询出只选修两门课程的学生学号和姓名 #20.查询出只选修两门课程的学生学号和姓名
SELECT st.id, st.`name`
FROM students st
WHERE (
SELECT COUNT(*)
FROM scores sc
WHERE sc.student_id = st.id
)=2;
#21.查询男生、女生人数 #21.查询男生、女生人数
SELECT st.gender, COUNT(*)
FROM students st
GROUP BY st.gender;
SELECT COUNT(IF(st.gender='男', TRUE, NULL)) '男生人数',
COUNT(IF(st.gender='女', TRUE, NULL)) '女生人数'
FROM students st;
#22.查询名字中含有「风」字的学生信息 #22.查询名字中含有「风」字的学生信息
SELECT *
FROM students st
WHERE st.`name` LIKE '%风%';
#23.查询同名同性学生名单，并统计同名人数 #23.查询同名同性学生名单，并统计同名人数
SELECT s.`name`, s.gender, COUNT(*)
FROM students s
GROUP BY s.`name`, s.gender
HAVING COUNT(*) > 1;
#24.查询 1990 年出生的学生名单 #24.查询 1990 年出生的学生名单
SELECT *
FROM students s
WHERE YEAR(s.birth) = 1990;
#25.查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列 #25.查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列