大家好，我是anyux。數(shù)據(jù)庫聯(lián)表查詢很重要，內(nèi)聯(lián)查詢更是尤為重要。

需要將school.sql文件導入到數(shù)據(jù)庫中

數(shù)據(jù)庫多表聯(lián)合查詢，school庫下表的邏輯結(jié)構(gòu)關系都在下圖中。可以通過驅(qū)動表加子表配合實現(xiàn)所有查詢要求。

統(tǒng)計zhang3,學習了幾門課

select STU.sname as 姓名, count(SC.sno) as 數(shù)量 from student as STU join sc as SC on STU.sno= SC.sno where STU.sname='zhang3';

查詢zhang3,學習的課程名稱有哪些?

方法1

select STU.sname as 姓名, COU.cname as 課程名 from student as STU join sc as SC on STU.sno = SC.sno join course as COU on SC.cno = COU.cno where STU.sname='zhang3';

方法2(推薦)

select STU.sname as 姓名, group_concat(COU.cname) as 課程名 from student as STU join sc as SC on STU.sno = SC.sno join course as COU on SC.cno = COU.cno where STU.sname='zhang3' group by STU.sname;

查詢KING老師教的學生名.

select TEA.tname as 教師名稱, group_concat(STU.sname) as 學生名稱 from teacher as TEA join course as COU on TEA.tno=COU.tno join sc as SC on SC.cno=COU.cno join student as STU on STU.sno=SC.sno where TEA.tname='KING' group by TEA.tname;

查詢KING所教課程的平均分數(shù)

select COU.cname as 課程名稱,TEA.tname as 教師名稱, avg(SC.score) as 課程成績 from teacher as TEA join course as COU on TEA.tno=COU.tno join sc as SC on SC.cno = COU.cno where TEA.tname='KING' group by COU.cname,TEA.tname;

每位老師所教課程的平均分,并按平均分排序

select TEA.tname as 教師名稱, COU.cname as 課程名稱, avg(SC.score) as 平均成績 from teacher as TEA join course as COU on TEA.tno=COU.tno join sc as SC on SC.cno=COU.cno group by TEA.tname, COU.cname order by AVG(SC.score) DESC;

查詢KING所教的不及格的學生姓名

select STU.sname as 學生姓名 from teacher as TEA join course as COU on TEA.tno=COU.tno join sc as SC on SC.cno=COU.cno join student as STU on STU.sno=SC.sno where TEA.tname='KING' and SC.score<60;

查詢所有老師所教學生不及格的信息

方法1

select TEA.tname as 教師名稱,STU.sname as 學生姓名,SC.score as 學生成績 from teacher as TEA join course as COU on TEA.tno=COU.tno join sc as SC on SC.cno=COU.cno join student as STU on STU.sno=SC.sno where SC.score<60;

方法2(推薦,顯示優(yōu)化)

select TEA.tname as 教師名稱,group_concat(concat(STU.sname,":",SC.score)) as 不及格的 from teacher as TEA join course as COU on TEA.tno=COU.tno join sc as SC on SC.cno=COU.cno join student as STU on STU.sno=SC.sno where SC.score<60 group by TEA.tno;

查詢平均成績大于60分的同學的學號和平均成績；

select STU.sno as 學號, avg(SC.score) as 平均成績 from student as STU join sc as SC on STU.sno=SC.sno group by STU.sno having avg(SC.score)>60;

查詢所有同學的學號、姓名、選課數(shù)、總成績；

select STU.sno as 學號, STU.sname as 姓名, count(SC.cno) as 選課數(shù), sum(SC.score) as 總成績 from student as STU join sc as SC on STU.sno=SC.sno group by STU.sno ;

查詢各科成績最高和最低的分：以如下形式顯示：課程ID，最高分，最低分

select sc.cno as 課程ID, max(sc.score) as 最高分,min(sc.score) as 最低分 from sc group by sc.cno;

統(tǒng)計各位老師,所教課程的及格率

select TEA.tname as 教師名稱,COU.cname as 課程名稱,concat((select count(sc.cno) from sc where sc.score>60)/(select count(sc.cno) from sc)*100,'%') as 及格率 from teacher as TEA join course as COU on TEA.tno=COU.tno join sc as SC on SC.cno=COU.cno group by TEA.tno,COU.cname;

查詢每門課程被選修的學生數(shù)

select COU.cno as 課程名稱, count(STU.sno) as 學生數(shù)量 from student as STU join sc as SC on STU.sno=SC.sno join course as COU on SC.cno=COU.cno group by COU.cno;

查詢出只選修了一門課程的全部學生的學號和姓名

select STU.sno as 學號,STU.sname as 學生名稱,count(SC.cno) as 選修課程數(shù)量 from student as STU join sc as SC on STU.sno=SC.sno group by SC.sno having count(SC.sno)=1;

查詢選修課程門數(shù)超過1門的學生信息

select STU.sno as 學號,STU.sname as 學生名稱,count(SC.cno) as 選修課程數(shù)量 from student as STU join sc as SC on STU.sno=SC.sno group by SC.sno having count(SC.sno)!=1;

統(tǒng)計每門課程:優(yōu)秀(85分以上),良好(70-85),一般(60-70),不及格(小于60)的學生列表

select STU.sname as 學生名稱,STU.sno as 學號,COU.cname as 課程名稱, case when SC.score>85 then '優(yōu)秀' when SC.score>70 and SC.score<=85 then '良好' when SC.score>=60 and SC.score<=70 then '一般' when SC.score<60 then '不及格' end as 成績狀態(tài) from student as STU join sc as SC on STU.sno=SC.sno join course as COU on SC.cno=COU.cno group by COU.cno,STU.sno,STU.sname,SC.score;

查詢平均成績大于85的所有學生的學號、姓名和平均成績

select STU.sno as 學號,STU.sname as 學生名稱, avg(SC.score) as 平均成績 from student as STU join sc as SC on STU.sno=SC.sno group by SC.score,STU.sname,STU.sno having avg(SC.score)>85;

總結(jié)

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