1 多表查詢 通過where 將表進行關聯

表human，student資料如下圖：

將兩表通過id欄位進行連線 輸出

select t1.id,t1.name,t1.age,t1.sex,t2.chinese,t2.math,t2.english from human as t1,student as t2 where t1.id  = t2.id;

2 檢視 view 資料只可檢視，不可操作

create view view1 as select t1.id,t1.name,t1.age,t1.sex,t2.chinese,t2.math,t2.english from human as t1,student as t2 where t1.id = t2.id;

3 sql語句綜合練習（表結構如下圖所示(學生表，課程表，分數表)）

3.1 分別查詢學生表和課程表中的全部資料；

select *from student;

select * from course;

3.2 查詢成績在70到80之間的學生學號，課程號和成績；

select id,cno,grade from sroce where grade >=70 and grade <= 80;

or: select id,cno,grade from sroce where grade between 70 and 80;

3.3 查詢291號課程成績最高分數;

select max(grade) from sroce where cno =291;

3.4 查詢學生都選修了哪些課程，要求列出課程號；

select  distinct(cno)  from course;

3.5 查詢291號課程所有學生的平均成績，最高成績，最低成績;

select avg(grade),max(grade),min(grade) from score where cno = 291;

3.6統計每個系的人數；

select dept,count(dept) from student group by dept;

3.7統計每門課程的修課人數和考試最高分；

select count(id),max(grade) from score group by cno;

3.8統計每個學生的選課門數，並按選課門數遞增顯示；

select count(id) from score group by id;

3.9 統計選修課的學生總數和考試的平均成績；

select count(id) ,avg(grade) from score;

3.10 查閱選修課數超過2門的學生的平均成績；

select avg(grade) ,count(cno)  as count from score group by cno having count >2 ;

3.11列出總成績超過200分的學生，要求列出學號，總成績；

select id,sum(grade) as sum_grade from score  group by id having sum_grade >200;

3.12 查詢選修了291課程學生的姓名和所在系；

select t1.name,t1.dept from student as t1,score as t2 where t1.id =t2.id  and cno = 291;

3.13 查詢成績80分以上的學生姓名，課程號和成績，並按成績降序排列；

select t1.name ,t2.cno,t2.grade from student as t1,sorce as t2 where t1.id = t2.id group by t2.id having grade > 80 order by grade desc;

3.13.1 查詢80分以上的學生；

select id ,cno,grade from score where grade > 80;

3.13.2 連線student 表，得到姓名；

select t1.name ,t2.cno,t2.grade  from student as t1, (select id, cno,grade from score where grade > 80) as t2 where t1.id =t2.id;

3.14 查詢計算機系男生修了‘數學’的學生姓名，成績；

select t1.name,t2.grade from student as t1,score as t2 where t1.id = t2.id and t1.dept = ‘computer’  and t1.sex = ‘man’;

3.15 查詢哪些學生的年齡相同，要求列出年齡相同的學生姓名和成績；

select t1.name ,t2.grade from student as t1 ,score as t2 where t1.id = t2.id group by t1.age;

3.16 分別查詢計算機系和數學系的學生姓名，性別，修課名稱，修課成績；

並要求將這兩個查詢結果合併成一個結果集；

並以系名，姓名，修課名稱，修課成績的順序顯示各列；

第一步：在student 表中獲得計算機系和數學系的學號，姓名，以及性別；

select id,name,sex from student where dept in(‘computer’,’math’);

第二步：與分數表相關聯，得到成績和課程號；

select  grade ,cno,t1.* from score as t1,( select id,name,sex from student where dept  in(‘computer’,’math’) ) as t2 where t1.id = t2.id;

第三步:與course關聯得到修課名稱；

select cname, t2.* from course as t1, (select  grade ,cno,t1.* from score as t1,( select id,name,sex from student where dept in(‘computer’,’math’) ) as t2 where t1.id = t2.id ) as t2 where t1.cno=t2.cno;

3.17 將計算機系成績高於80分的學生的修課情況插入到另一張表中，建立一個新表，然後插入資料。

create table temp as select t1.name,t3.cname from student as t1, score as t2,course as t3 where t1.id =t2.id and t1.dept = ‘computer’ and t2.cno = t3.cno and t2.grade > 80 ;

3.18 刪除修課成績小於60分的學生的修課記錄；

delete from score where grade < 60;

3.19 將所有選修了“c01”課程的學生的成績加10分；

update score set grade = grade + 10 where cno =291;