mysql查询案例
2021/5/4 2:25:26
本文主要是介绍mysql查询案例,对大家解决编程问题具有一定的参考价值,需要的程序猿们随着小编来一起学习吧!
#一、查询每个专业的学生人数 SELECT majorid,COUNT(*) FROM student GROUP BY majorid; #二、查询参加考试的学生中,每个学生的平均分、最高分 SELECT AVG(score),MAX(score),studentno FROM result GROUP BY studentno; #三、查询姓张的每个学生的最低分大于60的学号、姓名 SELECT s.studentno,s.`studentname`,MIN(score) FROM student s JOIN result r ON s.`studentno`=r.`studentno` WHERE s.`studentname` LIKE '张%' GROUP BY s.`studentno` HAVING MIN(score)>60; #四、查询每个专业生日在“1988-1-1”后的学生姓名、专业名称 SELECT m.`majorname`,s.`studentname` FROM student s JOIN major m ON m.`majorid`=s.`majorid` WHERE DATEDIFF(borndate,'1988-1-1')>0 GROUP BY m.`majorid`; #五、查询每个专业的男生人数和女生人数分别是多少 SELECT COUNT(*),sex,majorid FROM student GROUP BY sex,majorid; #六、查询专业和张翠山一样的学生的最低分 #①查询张翠山的专业编号 SELECT majorid FROM student WHERE studentname = '张翠山' #②查询编号=①的所有学生编号 SELECT studentno FROM student WHERE majorid=( SELECT majorid FROM student WHERE studentname = '张翠山' ) #②查询最低分 SELECT MIN(score) FROM result WHERE studentno IN( SELECT studentno FROM student WHERE majorid=( SELECT majorid FROM student WHERE studentname = '张翠山' ) ) #七、查询大于60分的学生的姓名、密码、专业名 SELECT studentname,loginpwd,majorname FROM student s JOIN major m ON s.majorid= m.majorid JOIN result r ON s.studentno=r.studentno WHERE r.score>60; #八、按邮箱位数分组,查询每组的学生个数 SELECT COUNT(*),LENGTH(email) FROM student GROUP BY LENGTH(email); #九、查询学生名、专业名、分数 SELECT studentname,score,majorname FROM student s JOIN major m ON s.majorid= m.majorid LEFT JOIN result r ON s.studentno=r.studentno #十、查询哪个专业没有学生,分别用左连接和右连接实现 #左 SELECT m.`majorid`,m.`majorname`,s.`studentno` FROM major m LEFT JOIN student s ON m.`majorid` = s.`majorid` WHERE s.`studentno` IS NULL; #右 SELECT m.`majorid`,m.`majorname`,s.`studentno` FROM student s RIGHT JOIN major m ON m.`majorid` = s.`majorid` WHERE s.`studentno` IS NULL; #十一、查询没有成绩的学生人数 SELECT COUNT(*) FROM student s LEFT JOIN result r ON s.`studentno` = r.`studentno` WHERE r.`id` IS NULL
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