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1,用于設定所select出來的數據是否允許出現重復行（完全相同的數據行）

all：允許出現——默認不寫就是All（允許的）。

distinct：不允許出現——就是所謂的“消除重復行”

2，where:條件

3，group by：分組依據 后面加表的字段名，通常只進行一個字段的分組

mysql表查詢語法形式：select [all | distinct] 字段名或表達式 from 表名 [where] [group by] [having] [order by] [limit];

練習題:共有下面四張表??? 學生表：student? 教師表：teacher? 課程表：course 成績表：score

????? ????

1，查詢Score表中至少有5名學生選修的并以3開頭的課程的平均分數

--操作表score，以cno分組并且cno是以3開頭，取出各個cno的總數，及與cno對應的degree的平均值

select count(cno),avg(degree) from score where cno like '3%' group by cno;

?

--從上面的虛擬表中找到cno總數大于5的

select * from

(select count(cno) a,avg(degree) b from score where cno like '3%' group by cno) c

where a>5;

2,查詢所有學生的Sno、Cname和Degree列

--找到student的sno
?select sno from student;

?--找到score 的sno,degree,cno
?select sno,degree,cno from score;

?--找到course的cno
?select cno,cname from course;

?--組成新表cno sno degree
?select a.cno,b.sno,b.sname,a.degree from (select sno,degree,cno from score) a? join (select sno,sname from student) b on a.sno=b.sno;

?--組成有cname cno sn degree sname的表
?select d.cname,e.cno,e.sno,e.degree,e.sname
?from
?? (select a.cno,b.sno,b.sname,a.degree from (select sno,degree,cno from score) a? join (select sno,sname from student) b on a.sno=b.sno) as e
? join
? (select cname,cno from course) as d
? on d.cno=e.cno;

3，查詢“95033”班學生的平均分

--從student取sno class,條件是class是95033的

select sno,class from student where class='95033';

--取出score中sno degree

select sno,degree from score;

--將上面兩張表組成一張,取degree的平均值

select avg(degree) from

(select sno,class from student where class='95033') a

join

(select sno,degree from score) b

on a.sno=b.sno;

4,查詢選修“3-105”課程的成績高于“109”號同學成績的所有同學的記錄

--將109號的成績取出

select degree from score where sno='109' and cno='3-105';

-- 得出最終表

select * from score

where

degree>(select degree from score where sno='109' and cno='3-105')

and cno='3-105';

5,查詢和學號為108的同學同年出生的所有學生的Sno、Sname和Sbirthday列

--找到student中sno為108 的Sbirthday
select year(sbirthday) from student where sno='108';

-- 得出最終表
select sno,sname,sbirthday from student

where

year(sbirthday)=(select year(sbirthday) from student where sno='108');

?6.查詢“張旭“教師任課的學生成績（姓名）

--找到teacher中tname為張旭的tno

select tno from teacher where tname='張旭';

--找到course中tno和teacher中tname為張旭的tno相同的cno

select cno from course where tno=(select tno from teacher where tname='張旭');

--找到score中cno為6-166的sno cno degree

select sno,cno,degree from score

where

cno=(select cno from course where tno=(select tno from teacher where tname='張旭'));

--找到student表中與上表sno相同的sname與上表組成新表

select a.sname,b.sno,b.cno,b.degree from

(select sno,sname from student) a

join

(select sno sno,cno,degree from score where cno=(select cno from course where tno=(select tno from teacher where tname='張旭'))) b

on a.sno=b.sno;

7,查詢考計算機導論的學生成績
--找到course中cname為計算機導論的cno
select cno from course where cname='計算機導論';

--找到score中cno與上表中相同時的sno degree
select sno,degree from score where cno=(select cno from course where cname='計算機導論');

-- 得出最終表
select b.sname,a.sno,a.degree from

(select sno,degree from score where

cno=(select cno from course where cname='計算機導論')) a join (select sname,sno from student) b

on a.sno=b.sno;

8,查詢李誠老師教的課程名稱
select tno from teacher where tname='李誠';
select cname,cno from course where tno=(select tno from teacher? where tname='李誠');

9,查詢選修某課程的同學人數多于5人的教師姓名
--score以cno分組，統計cno的數量
select count(cno) a,cno from score group by cno;

--找到上表中cno數量大于5的的cno
select cno from (select count(cno) a,cno from score group by cno) b where a>5;

--找到與上表cno一致的表course表中的tno
select tno from course where cno=(select cno from (select count(cno) a,cno from score group by cno) b where a>5);

--與上表tno一致的表teacher中的tname
select tname from teacher where tno=(select tno from course where cno=(select cno from (select count(cno) a,cno from score group by cno) b where a>5));

10,查詢95033班和95031班全體學生的記錄
--找到表score中的sno和cno 和degree
select sno,cno,degree from score;
--將上表和student組合
select a.sno,a.sname,a.ssex,a.sbirthday,a.class,b.cno,b.degree from

(select * from student) a join (select cno,degree,sno from score) b

on a.sno=b.sno;

11,查詢存在有85分以上成績的課程Cno
select cno,degree from score where degree>85;

12,查詢出“計算機系“教師所教課程的成績表
--找到teacher中的tno tname
select tno,tname from teacher where dapart='計算機系';
--找到course中tno和上表相同的cno
select a.cno,b.tno,b.tname from (select tno,cno from course) a join (select tno,tname from teacher where dapart='計算機系') b on a.tno=b.tno;
--找到score中cno與上表相同的degree
select c.sno,c.cno,c.degree,d.tname from (select sno,cno,degree from score) c join (select a.cno,b.tno,b.tname from (select tno,cno from course) a join (select tno,tname from teacher where dapart='計算機系') b on a.tno=b.tno) d on c.cno=d.cno;

13,查詢選修編號為“3-105“課程且成績至少高于選修編號為“3-245”的同學?? ?的Cno、Sno和Degree,并按Degree從高到低次序排序
--score中找到cno=3-245的degree,取出最小值
select min(degree) from score where cno='3-245';
--score中找到cno=3-105的cno sno degree，并且degree大于上表的degree
select cno,sno,degree from

score where cno='3-105'

and degree>(select min(degree) from score where cno='3-245')

order by degree desc;

14,查詢選修編號為“3-105”且成績高于選修編號為“3-245”課程的同學的?? ?Cno、Sno和Degree.
--找到score中cno=3-245中的degree的最大值
select max(degree) from score where cno='3-245';
--找到score中cno=3-105的cno sno degree
select cno,sno,degree from

score where

degree>(select max(degree) from score where cno='3-245') order by degree asc;

15,查詢所有教師和同學的name、sex和birthday
select tname,tsex,tbirthday from teacher
union
select sname,ssex,sbirthday from student;
16,查詢所有“女”教師和“女”同學的name、sex和birthday
select tname,tsex,tbirthday from teacher where tsex='女'
union
select sname,ssex,sbirthday from student where ssex='女';

17,查詢成績比該課程平均成績低的同學的成績表
select avg(degree) from score where cno='3-105';
select avg(degree) from score where cno='3-245';
select avg(degree) from score where cno='6-166';
select * from score where cno='3-105' and degree<(select avg(degree) from score where cno='3-105')
union
select * from score where cno='3-245' and degree<(select avg(degree) from score where cno='3-245')
union
select * from score where cno='6-166' and degree<(select avg(degree) from score where cno='6-166');

18,查詢所有任課教師的Tname和Depart
select a.tname,a.dapart from
(select tno,tname,dapart from teacher) a join
(select tno from course) b
on a.tno=b.tno;

19,查詢所有未講課的教師的Tname和Depart
select a.tname,a.dapart from
(select tno,tname,dapart from teacher) a join
(select tno from course) b
on a.tno=b.tno;

20,查詢至少有2名男生的班號
select count(ssex),class from student where ssex='男' group by class;

select b.class from (select count(ssex) a,class from student where ssex='男' group by class) b where a>=2;

21,查詢Student表中不姓“王”的同學記錄
select * from student where sname not like '王%';

22,查詢Student表中每個學生的姓名和年齡
select? sname,year(now())-year(sbirthday) from student;

23,查詢Student表中最大和最小的Sbirthday日期值
select min(day(sbirthday)),max(day(sbirthday)) from student;

24,以班號和年齡從大到小的順序查詢Student表中的全部記錄
select * from student order by class desc,date(sbirthday) asc;

25,查詢“男”教師及其所上的課程
select tno from teacher where tsex='男';
select a.tno,b.cname,a.tname from (select tno,tname from teacher where tsex='男') a join (select * from course) b on a.tno=b.tno;

?

轉載于:https://www.cnblogs.com/wfc139/p/8939605.html

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