mysql建表規則和基本使用語法

數據庫的設計范式數據庫的設計范式

1. 要求：每一個分量必須是不可分的數據項。

   特點：

   1）有主鍵，且主鍵不能為空。

   2）字段不能再分。

    

   2.第二范式（2NF）

   要求：在范式一的基礎上，且每一個非主屬性完全函數依賴於主鍵。

   特點：

   1）滿足第一范式。

   2）表中的每一個非主屬性，必須完全依賴於本表主鍵。

   3）只有當一個表中，主鍵由兩個或以上的屬性組成的時候，才會出現不符合第二范式的情況。(如果出現不完全依賴那么只能發生在聯合主鍵的情況下。

3.第三范式（3NF）

要求：在第二范式的基礎上，且消除傳遞依賴性1）滿足第二范式

2）所有的非主鍵列依賴於主鍵列

注：3NF是對字段冗余性的約束，即任何字段不能由其他字段派生出來，它要求字段沒有冗余，但是沒有數據冗余的數據庫並不一定是最好的數據庫，所以有沒有冗余的設計，要綜合來考慮

 

-----mysql的查詢語句練習

 

學生表 student 學號 姓名  性別 出生年月日  所在班級
create table student(
    sno varchar(20) primary key,
        sname varchar(20) not null,
        ssex varchar(12) not null,
        sbirthday datetime,
        cla int(12)
    );
insert into student values("101","曾華","男","1977-09-01","95033");
insert into student values("102","匡明","男","1975-10-02","95031");
insert into student values("103","王麗","女","1976-01-23","95033");
insert into student values("105","匡yi明","男","1975-10-02","95031");
insert into student values("104","王er麗","女","1976-01-23","95033");
insert into student values("106","陸君","男","1974-06-03","95031");
​
​

--課程表 course 課程號 課程名稱 教師編號
表的約束--外鍵約束 foreign key reference 
1 外鍵約束
一個表中某字段的值，受另一張表中某個字段的限制
主表（父表）：提供數據的表
從表（子表）：外鍵所在的表（引用主表中唯一性字段（主健，唯一）的值）
外鍵的值只能是主表中對應字段的值或者為null
foreign key references 主表(字段) --無名
constraint 約束名 foreign key references 主表(字段) -- 有名
foreign key references 主表(字段)   
constraint 約束名 foreign key references 主表(字段)
---------------------------------------
        create table course(
            cno varchar(20) primary key,
            cname varchar(20) not null,
            tno varchar(20) not null,
            foreign key(tno) references teacher(tno)
​
        );
        
 insert into course values("3-105","計算機導論","825");
 insert into course values("6-166","數字電路","856");
 insert into course values("9-888","高等數學","831");
​

教師表 teacher 教師編號 教師名字 教師性別 出生年月日 職稱所在部門
​
create table teacher(
    tno varchar(20) primary key,
        tname varchar(20) not null,
        tsex varchar(10) not null,
        tbirthday datetime,
        prof varchar(20) not null,
        depart varchar(20) not null
    );
    insert into teacher values("804","李誠","男","1958-12-02","副教授","計算機系");
     insert into teacher values("856","張旭","男","1969-03-12","講師","電子工程系");
     insert into teacher values("825","王萍","女","1972-05-05","助教","計算機系");
     insert into teacher values("831","劉冰","女","1977-08-14","副教授","電子工程系");
​
​

– 成績表
– Score
– 學號
– 課程號
– 成績
-----------drop table score;
create table score(
sno varchar(20) not null,
    cno varchar(20) not null,
    grade decimal,
    foreign key(sno) references student(sno),
    foreign key(cno) references course(cno),
    primary key(sno,cno)
);
insert into score values("103","3-105","92");
insert into score values("103","6-166","85");
insert into score values("103","9-888","86");
insert into score values("105","3-105","88");
insert into score values("105","6-166","79");
insert into score values("105","9-888","75");
insert into score values("106","3-105","76");
insert into score values("106","6-166","81");
insert into score values("106","9-888","68");
​
​
​

 

sql 查詢語句
select * from student; 查詢student中的所有數據
select sname from student; 查詢student中的sname字段的值
select distinct depart from teacher; 查詢教師所有的單位既不重復的depart的值 -- distinct 去重
-- 查詢score表中的成績在60-80的所有記錄。
-- 查詢區間 between...and
select * from score where 60<grade<80;
select * from score where grade between 60 and 80;
-- 查詢 score 表中成績為85，86或88的紀錄。
-- 表示或者的關系查詢 in
select * from score where grade in(85,86,88);
mysql> select * from score where grade in(85,86,88);
        +-----+-------+-------+
        | sno | cno   | grade |
        +-----+-------+-------+
        | 103 | 6-166 |    85 |
        | 103 | 9-888 |    86 |
        | 105 | 3-105 |    88 |
        +-----+-------+-------+
        3 rows in set (0.00 sec)
        
-- 查詢student表中'96031'班或性別為女的同學紀錄
-- or表示或者
select * from student where class='95031' or ssex='女';
-- 以cla降序查詢student表中的所有記錄。
-- 升序order by asc 降序 order by desc
 select * from student order by cla desc;
-- 以cno升序，degree降序查詢score 表中的所有記錄
select * from score order by cno asc,grade desc;
mysql> select * from score order by cno asc,grade desc;
        +-----+-------+-------+
        | sno | cno   | grade |
        +-----+-------+-------+
        | 103 | 3-105 |    92 |
        | 105 | 3-105 |    88 |
        | 106 | 3-105 |    76 |
        | 103 | 6-166 |    85 |
        | 106 | 6-166 |    81 |
        | 105 | 6-166 |    79 |
        | 103 | 9-888 |    86 |
        | 105 | 9-888 |    75 |
        | 106 | 9-888 |    68 |
        +-----+-------+-------+
        9 rows in set (0.00 sec)
-- 查詢'95031'班的學生人數。
-- 統計count
select count(*) from student where cla='95031';
        mysql> select count(*) from student where cla='95031';
            +----------+
            | count(*) |
            +----------+
            |        3 |
            +----------+
            1 row in set (0.00 sec)
    
-- 查詢score表中的最高分的學生學號和課程號。（子查詢或者排序）
-- 分析：找到最高分 select max(grade) from score;
-- 找到最高分的sno,cno 
        select sno,cno from score where grade=(select max(grade) from score);
    -- 排序分析：limit 0,1 0表示開始索引,1表示取幾個
    -- select sno,cno,grade from score order by grade;
    -- select sno,cno,grade from score order by grade desc limit 0,1;
            mysql> select sno,cno from score where grade=(select max(grade) from score);
        +-----+-------+
        | sno | cno   |
        +-----+-------+
        | 103 | 3-105 |
        +-----+-------+
        1 row in set (0.00 sec)
​
-- 查詢每門課的平均成績
-- avg(grade)
   select avg(grade) from score where cno='9-888';
            mysql> select avg(grade) from score where cno='9-888';
            +------------+
            | avg(grade) |
            +------------+
            |    76.3333 |
            +------------+
            1 row in set (0.00 sec)
   -- 查詢每門課
   -- group by 分組
   select cno,avg(grade) from score group by cno;
mysql> select cno,avg(grade) from score group by cno;
        +-------+------------+
        | cno   | avg(grade) |
        +-------+------------+
        | 3-105 |    85.3333 |
        | 6-166 |    81.6667 |
        | 9-888 |    76.3333 |
        +-------+------------+
        3 rows in set (0.00 sec)
        
 -- 查詢score表中至少有2名學生選修的並以3開頭的平均分數
 -- where、聚合函數、having 在from后面的執行順序：
-- where>聚合函數(sum,min,max,avg,count)>having
 -- having條件 若須引入聚合函數來對group by 結果進行過濾 則只能用having 
 -- like 模糊查詢 類似正則
 -- 分析：先分組 select cno,avg(grade) from score group by cno
 -- 第二步 having count(2)>=2
 -- 第三步 and cno like '3%';
 select cno,avg(grade),count(*) from score group by cno having count(cno)>=2 and cno like '3%';

 注意：
 1、where 后不能跟聚合函數，因為where執行順序大於聚合函數。
2、where 子句的作用是在對查詢結果進行分組前，將不符合where條件的行去掉，即在分組之前過濾數據，條件中不能包含聚組函數，使用where條件顯示特定的行。
3、having 子句的作用是篩選滿足條件的組，即在分組之后過濾數據，條件中經常包含聚組函數，使用having 條件顯示特定的組，也可以使用多個分組標准進行分組。
​
-- 查詢分數大於70，小於90的sno列。
select sno grade from score where 70<grade<90;
select sno grade from score where grade between 70 and 90;
    
-- 查詢所有學生的sname,cno 和grade列
select sname,cno,grade from student as st,score as sc where st.sno=sc.sno;
mysql>  select sname,cno,grade from student as st,score as sc where st.sno=sc.sno;
        +--------+-------+-------+
        | sname  | cno   | grade |
        +--------+-------+-------+
        | 王麗       | 3-105 |    92 |
        | 王麗       | 6-166 |    85 |
        | 王麗       | 9-888 |    86 |
        | 匡yi明     | 3-105 |    88 |
        | 匡yi明     | 6-166 |    79 |
        | 匡yi明     | 9-888 |    75 |
        | 陸君      | 3-105 |    76 |
        | 陸君      | 6-166 |    81 |
        | 陸君      | 9-888 |    68 |
        +--------+-------+-------+
        9 rows in set (0.00 sec)
        
-- 查詢所有學生的sno，cname和grade列 course cname score sno and grade
 select sno,cname,grade from course as c,score as s where c.cno=s.cno;
 mysql> select sno,cname,grade from course as c,score as s where c.cno=s.cno;
    +-----+------------+-------+
    | sno | cname      | grade |
    +-----+------------+-------+
    | 103 | 計算機導論           |    92 |
    | 103 | 數字電路         |    85 |
    | 103 | 高等數學         |    86 |
    | 105 | 計算機導論           |    88 |
    | 105 | 數字電路         |    79 |
    | 105 | 高等數學         |    75 |
    | 106 | 計算機導論           |    76 |
    | 106 | 數字電路         |    81 |
    | 106 | 高等數學         |    68 |
    +-----+------------+-------+
    9 rows in set (0.00 sec)

-- 查詢所有學生的sname，cname和grade列
-- sname--student cname--course grade--score
select sname,cname,grade from student as st,course as c,score as sc where c.cno=sc.cno and st.sno=sc.sno;
mysql> select sname,cname,grade from student as st,course as c,s
 c.cno=sc.cno and st.sno=sc.sno;
    +--------+------------+-------+
    | sname  | cname      | grade |
    +--------+------------+-------+
    | 王麗       | 計算機導論           |    92 |
    | 王麗       | 數字電路         |    85 |
    | 王麗       | 高等數學         |    86 |
    | 匡yi明     | 計算機導論           |    88 |
    | 匡yi明     | 數字電路         |    79 |
    | 匡yi明     | 高等數學         |    75 |
    | 陸君      | 計算機導論           |    76 |
    | 陸君      | 數字電路         |    81 |
    | 陸君      | 高等數學         |    68 |
    +--------+------------+-------+
    9 rows in set (0.00 sec)
​
-- 查詢95031班的學生每門課的平均分數 avg()平均分時
-- in 表示或的關系
-- cla-95031--student表 grade--score表 課程名稱 cname--course
select avg(grade),cno from score where sno in (select sno from student where cla='95031') group by cno;
select cla,avg(grade),cname from student as st,course as co,score as sc where st.sno=sc.sno and co.cno=sc.cno;

-- 查詢選修3-105課程的成績高於106號同學3-105成績的所有同學的記錄
select grade from score where sno='106' and cno='3-105';
select * from score where cno='3-105' and grade>(select grade from score where sno='106' and cno='3-105');
mysql> select * from score where cno='3-105' and grade>(select grade from score
where sno='106' and cno='3-105');
+-----+-------+-------+
| sno | cno   | grade |
+-----+-------+-------+
| 103 | 3-105 |    92 |
| 105 | 3-105 |    88 |
+-----+-------+-------+
2 rows in set (0.00 sec)
​
-- 查詢成績高於學號106課程為3-105的成績的所有記錄
select * from score where grade>(select grade from score where sno='106' and cno='3-105');

-- 查詢學號為108,101的同學同年出生的所有學生的sno，sname和sbirthday列。
-- 只要查年份 year(sbirthday)
select * from student where year(sbirthday) in (select year(sbirthday) from student where sno in (101,103));
​
-- 查詢張旭教師任課的學生成績。
select * from teacher where tname ='張旭';
select cno from course where tno=(select * from teacher where tname ='張旭');

-- 查詢選修某課程的同學人數多於3人的教師姓名
select cno from score group by cno having count(*)>2;
select tname from teacher where tno=(select tno from course where cno=(select cno from score group by cno having count(*)>3));

-- 查詢95033班和95031班的全體學生的記錄
select * from student where cla in ('95033','95031');
​
-- 查詢存在有85分以上成績的課程cno.
select cno from score where grade>85;
​
-- 查詢出計算機系教師所教課程的成績表。
select * from score where cno in (select cno from course where tno in (select tno from teacher where depart="計算機系"));

-- 查詢計算機系和電子工程系不同職稱的教師的tname和prof。
-- union 求並集
select prof from teacher where depart='電子工程系';
select * from teacher where depart='計算機系' and prof not in(select prof from teacher where depart='電子工程系')
union
select * from teacher where depart='電子工程系' and prof not in(select prof from teacher where depart='計算機系');

mysql> select * from teacher where depart='計算機系' and prof not in(select pro
 from teacher where depart='電子工程系')
    ->  union
    ->  select * from teacher where depart='電子工程系' and prof not in(select
rof from teacher where depart='計算機系');
+-----+-------+------+---------------------+------+------------+
| tno | tname | tsex | tbirthday           | prof | depart     |
+-----+-------+------+---------------------+------+------------+
| 825 | 王萍     | 女    | 1972-05-05 00:00:00 | 助教     | 計算機系          |
| 856 | 張旭      | 男     | 1969-03-12 00:00:00 | 講師    | 電子工程系
|
+-----+-------+------+---------------------+------+------------+
2 rows in set (0.00 sec)
​
-- 查詢選修編號為3-105課程且成績至少高於選修編號為3-166的同學的cno，sno和grade,且成績從高到低次序排列。
-- any 大於其中至少一個
select * from score where cno='6-166';
select * from score where cno='3-105';
select * from score where cno='3-105' and grade>any(select grade from score where cno='6-166')
order by grade desc;

-- 查詢選修編號為3-105課程且成績至少高於選修編號為3-166的同學的cno，sno和grade
-- all 表示所有
​
select * from score where cno='6-166';
select * from score where cno='3-105';
select * from score where cno='3-105' and grade>all(select grade from score where cno='6-166');
​
-- 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;
​
-- 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';
​
-- 查詢成績比該課程平均成績低的同學的成績表。
-- 復制表score為表a和表b
select con,avg(grade) from score group by cno;
select * from score a where grade<(select avg(grade) from score b where a.cno = b.cno);
mysql>  select * from score a where grade<(select avg(grade) from score b where
a.cno = b.cno);
+-----+-------+-------+
| sno | cno   | grade |
+-----+-------+-------+
| 105 | 6-166 |    79 |
| 105 | 9-888 |    75 |
| 106 | 3-105 |    76 |
| 106 | 6-166 |    81 |
| 106 | 9-888 |    68 |
+-----+-------+-------+
5 rows in set (0.00 sec)
​
-- 查詢所有任課教師的tname和depart
select tname,depart from teacher where tno in (select tno from course);

-- 查詢至少有倆名男生的班號。
select cla from student where ssex='男' group by cla having count(*)>1;
​
-- 查詢student表中不性王的同學記錄。
select * from student;
select * from student where sname not like '王%';
​
-- 查詢student表中每個學生的姓名和年齡
-- year(now()) 查看當前年份
select sname,year(now())-year(sbirthday) from student;

-- 查詢student表中最大值和最小的birthday的日期值
select max(sbirthday) as '最大值',min(sbirthday) as '最小值' from student;
mysql> select max(sbirthday) as '最大值',min(sbirthday) as '最小值' from student
            ;
            +---------------------+---------------------+
            | 最大值                   | 最小值                  |
            +---------------------+---------------------+
            | 1977-09-01 00:00:00 | 1974-06-03 00:00:00 |
            +---------------------+---------------------+
            1 row in set (0.00 sec)
         
-- 以班號和年齡從大到小的順序查詢studente表中的全部記錄。
select * from student order by cla desc,sbirthday;
​
-- 查詢男教師及其所上的課程
select * from course where tno in (select tno from teacher where tsex='男');

-- 查詢最高分同學的sno,cno,和grade.
select * from score where grade=(select max(grade) from score);
​
-- 查詢和王麗同性別的所有同學的sname
select ssex from student where sname='王麗';
select sname from student where ssex=(select ssex from student where sname='王麗');
​
-- 查詢和王麗同性別並在同班的同學sname
select ssex from student where sname='王麗';
select sname from student where ssex=(select ssex from student where sname='王麗') and cla=(select cla from student where sname='王麗');
​
-- 查詢所有選修計算機導論課程的男同學的成績表。
select * from student where ssex='男';
    select * from course where cname='計算機導論';
    select * from score where cno=(select cno from course where cname='計算機導論') and sno in (select sno from student where ssex='男');
  
-- 假設用如下命令建立了一個grade表
create table gradeq(
low int(3),
    upp int(3),
    gradet char(1)
);
insert into gradeq values(90,100,'A');
insert into gradeq values(80,90,'B');
insert into gradeq values(70,80,'C');
insert into gradeq values(60,70,'D');
insert into gradeq values(50,60,'E');
  -- 先查詢所有學生的sno cno 和 gradet列
  select sno,cno,gradet from score,gradeq where grade between low and upp;
  mysql> select sno,cno,gradet from score,gradeq where grade between low and upp;
+-----+-------+--------+
| sno | cno   | gradet |
+-----+-------+--------+
| 101 | 3-105 | A      |
| 103 | 3-105 | A      |
| 103 | 6-166 | B      |
| 103 | 9-888 | B      |
| 105 | 3-105 | B      |
| 105 | 6-166 | C      |
| 105 | 9-888 | C      |
| 106 | 3-105 | C      |
| 106 | 6-166 | B      |
| 106 | 9-888 | D      |
+-----+-------+--------+
10 rows in set (0.00 sec)

sql 的四種連接查詢
-- 內連接 inner join 或者 join
-- 外連接 
-- 左連接 left join 或者 left outer join
-- 有連接 right join 或者 right outer join 
-- 完全外連接 full 或者 full outer join

創建倆個表
person表 id,name,cardId
create table person(
    id int,
        name varchar(20),
        cardId int
    );
    insert into person values(1,'張三',1);
    insert into person values(2,'李四',3);
    insert into person values(3,'王五',6);
    insert into person values(4,'馬六',9);

card表 id,name
    create table card(
    id int,
        name varchar(20)
    );
    
    insert into card values(1,'飯卡');
    insert into card values(2,'中國卡');
    insert into card values(3,'交通卡');
    insert into card values(4,'招商卡');
    insert into card values(5,'平安卡');
    
-- 並沒有創建外鍵
-- inner join 查詢(內連接) 或者可以使用join
-- 代碼解析：倆張表連接以后使得cardId=id使用inner join 來連接
-- join 左右是我們關聯的表 后跟on 后面的是條件
select * from person inner join card on person.cardId=card.id;
mysql> select * from person inner join card on person.cardId=card.id;
        +------+------+--------+------+--------+
        | id   | name | cardId | id   | name   |
        +------+------+--------+------+--------+
        |    1 | 張三     |      1 |    1 | 飯卡       |
        |    2 | 李四     |      3 |    3 | 交通卡      |
        +------+------+--------+------+--------+
        2 rows in set (0.00 sec)
        
-- left join 外連接（左連接）或者 left outer join
select * from person left join card on person.cardId=card.id;
mysql> select * from person left join card on person.cardId=card.id;
    +------+------+--------+------+--------+
    | id   | name | cardId | id   | name   |
    +------+------+--------+------+--------+
    |    1 | 張三     |      1 |    1 | 飯卡       |
    |    2 | 李四     |      3 |    3 | 交通卡      |
    |    3 | 王五     |      6 | NULL | NULL   |
    |    4 | 馬六     |      9 | NULL | NULL   |
    +------+------+--------+------+--------+
    4 rows in set (0.00 sec)
    -- 左外連接,會把左面的數據全都拿出來，而又變得數據條件相等的拿，不等的補NULL
    
-- right join 外連接(右鏈接) 或者 right outer join
select * from person right join card on person.cardId=card.id;
mysql>  select * from person right join card on person.cardId=card.id;
        +------+------+--------+------+--------+
        | id   | name | cardId | id   | name   |
        +------+------+--------+------+--------+
        |    1 | 張三     |      1 |    1 | 飯卡       |
        | NULL | NULL |   NULL |    2 | 中國卡      |
        |    2 | 李四     |      3 |    3 | 交通卡      |
        | NULL | NULL |   NULL |    4 | 招商卡      |
        | NULL | NULL |   NULL |    5 | 平安卡      |
        +------+------+--------+------+--------+
        5 rows in set (0.00 sec)
       -- 右外連接,會把右面的數據全都拿出來，而又變得數據條件相等的拿，不等的補NULL 
​
-- full join 全外連接 
----------- mysql 不支持 full join 外連接 ---------
select * from person full join card on person.cardId=card.id;
-- 所以mysql如果需要實現全外連接就需要用左連接union有鏈接即可
select * from person right join card on person.cardId=card.id
union
select * from person left join card on person.cardId=card.id;
mysql> select * from person right join card on person.cardId=card.id
    ->  union
   ->  select * from person left join card on person.cardId=card.id;
        +------+------+--------+------+--------+
        | id   | name | cardId | id   | name   |
        +------+------+--------+------+--------+
        |    1 | 張三     |      1 |    1 | 飯卡       |
        | NULL | NULL |   NULL |    2 | 中國卡      |
        |    2 | 李四     |      3 |    3 | 交通卡      |
        | NULL | NULL |   NULL |    4 | 招商卡      |
        | NULL | NULL |   NULL |    5 | 平安卡      |
        |    3 | 王五     |      6 | NULL | NULL   |
        |    4 | 馬六     |      9 | NULL | NULL   |
        +------+------+--------+------+--------+
        7 rows in set (0.00 sec)

 

數據庫的設計范式

1. 要求：每一個分量必須是不可分的數據項。

   特點：

   1）有主鍵，且主鍵不能為空。

   2）字段不能再分。

    

   2.第二范式（2NF）

   要求：在范式一的基礎上，且每一個非主屬性完全函數依賴於主鍵。

   特點：

   1）滿足第一范式。

   2）表中的每一個非主屬性，必須完全依賴於本表主鍵。

   3）只有當一個表中，主鍵由兩個或以上的屬性組成的時候，才會出現不符合第二范式的情況。(如果出現不完全依賴那么只能發生在聯合主鍵的情況下。

3.第三范式（3NF）

要求：在第二范式的基礎上，且消除傳遞依賴性1）滿足第二范式

2）所有的非主鍵列依賴於主鍵列

注：3NF是對字段冗余性的約束，即任何字段不能由其他字段派生出來，它要求字段沒有冗余，但是沒有數據冗余的數據庫並不一定是最好的數據庫，所以有沒有冗余的設計，要綜合來考慮

 

-----mysql的查詢語句練習

 

學生表 student 學號 姓名  性別 出生年月日  所在班級
create table student(
    sno varchar(20) primary key,
        sname varchar(20) not null,
        ssex varchar(12) not null,
        sbirthday datetime,
        cla int(12)
    );
insert into student values("101","曾華","男","1977-09-01","95033");
insert into student values("102","匡明","男","1975-10-02","95031");
insert into student values("103","王麗","女","1976-01-23","95033");
insert into student values("105","匡yi明","男","1975-10-02","95031");
insert into student values("104","王er麗","女","1976-01-23","95033");
insert into student values("106","陸君","男","1974-06-03","95031");
​
​

--課程表 course 課程號 課程名稱 教師編號
表的約束--外鍵約束 foreign key reference 
1 外鍵約束
一個表中某字段的值，受另一張表中某個字段的限制
主表（父表）：提供數據的表
從表（子表）：外鍵所在的表（引用主表中唯一性字段（主健，唯一）的值）
外鍵的值只能是主表中對應字段的值或者為null
foreign key references 主表(字段) --無名
constraint 約束名 foreign key references 主表(字段) -- 有名
foreign key references 主表(字段)   
constraint 約束名 foreign key references 主表(字段)
---------------------------------------
        create table course(
            cno varchar(20) primary key,
            cname varchar(20) not null,
            tno varchar(20) not null,
            foreign key(tno) references teacher(tno)
​
        );
        
 insert into course values("3-105","計算機導論","825");
 insert into course values("6-166","數字電路","856");
 insert into course values("9-888","高等數學","831");
​

教師表 teacher 教師編號 教師名字 教師性別 出生年月日 職稱所在部門
​
create table teacher(
    tno varchar(20) primary key,
        tname varchar(20) not null,
        tsex varchar(10) not null,
        tbirthday datetime,
        prof varchar(20) not null,
        depart varchar(20) not null
    );
    insert into teacher values("804","李誠","男","1958-12-02","副教授","計算機系");
     insert into teacher values("856","張旭","男","1969-03-12","講師","電子工程系");
     insert into teacher values("825","王萍","女","1972-05-05","助教","計算機系");
     insert into teacher values("831","劉冰","女","1977-08-14","副教授","電子工程系");
​
​

– 成績表
– Score
– 學號
– 課程號
– 成績
-----------drop table score;
create table score(
sno varchar(20) not null,
    cno varchar(20) not null,
    grade decimal,
    foreign key(sno) references student(sno),
    foreign key(cno) references course(cno),
    primary key(sno,cno)
);
insert into score values("103","3-105","92");
insert into score values("103","6-166","85");
insert into score values("103","9-888","86");
insert into score values("105","3-105","88");
insert into score values("105","6-166","79");
insert into score values("105","9-888","75");
insert into score values("106","3-105","76");
insert into score values("106","6-166","81");
insert into score values("106","9-888","68");
​
​
​

 

sql 查詢語句
select * from student; 查詢student中的所有數據
select sname from student; 查詢student中的sname字段的值
select distinct depart from teacher; 查詢教師所有的單位既不重復的depart的值 -- distinct 去重
-- 查詢score表中的成績在60-80的所有記錄。
-- 查詢區間 between...and
select * from score where 60<grade<80;
select * from score where grade between 60 and 80;
-- 查詢 score 表中成績為85，86或88的紀錄。
-- 表示或者的關系查詢 in
select * from score where grade in(85,86,88);
mysql> select * from score where grade in(85,86,88);
        +-----+-------+-------+
        | sno | cno   | grade |
        +-----+-------+-------+
        | 103 | 6-166 |    85 |
        | 103 | 9-888 |    86 |
        | 105 | 3-105 |    88 |
        +-----+-------+-------+
        3 rows in set (0.00 sec)
        
-- 查詢student表中'96031'班或性別為女的同學紀錄
-- or表示或者
select * from student where class='95031' or ssex='女';
-- 以cla降序查詢student表中的所有記錄。
-- 升序order by asc 降序 order by desc
 select * from student order by cla desc;
-- 以cno升序，degree降序查詢score 表中的所有記錄
select * from score order by cno asc,grade desc;
mysql> select * from score order by cno asc,grade desc;
        +-----+-------+-------+
        | sno | cno   | grade |
        +-----+-------+-------+
        | 103 | 3-105 |    92 |
        | 105 | 3-105 |    88 |
        | 106 | 3-105 |    76 |
        | 103 | 6-166 |    85 |
        | 106 | 6-166 |    81 |
        | 105 | 6-166 |    79 |
        | 103 | 9-888 |    86 |
        | 105 | 9-888 |    75 |
        | 106 | 9-888 |    68 |
        +-----+-------+-------+
        9 rows in set (0.00 sec)
-- 查詢'95031'班的學生人數。
-- 統計count
select count(*) from student where cla='95031';
        mysql> select count(*) from student where cla='95031';
            +----------+
            | count(*) |
            +----------+
            |        3 |
            +----------+
            1 row in set (0.00 sec)
    
-- 查詢score表中的最高分的學生學號和課程號。（子查詢或者排序）
-- 分析：找到最高分 select max(grade) from score;
-- 找到最高分的sno,cno 
        select sno,cno from score where grade=(select max(grade) from score);
    -- 排序分析：limit 0,1 0表示開始索引,1表示取幾個
    -- select sno,cno,grade from score order by grade;
    -- select sno,cno,grade from score order by grade desc limit 0,1;
            mysql> select sno,cno from score where grade=(select max(grade) from score);
        +-----+-------+
        | sno | cno   |
        +-----+-------+
        | 103 | 3-105 |
        +-----+-------+
        1 row in set (0.00 sec)
​
-- 查詢每門課的平均成績
-- avg(grade)
   select avg(grade) from score where cno='9-888';
            mysql> select avg(grade) from score where cno='9-888';
            +------------+
            | avg(grade) |
            +------------+
            |    76.3333 |
            +------------+
            1 row in set (0.00 sec)
   -- 查詢每門課
   -- group by 分組
   select cno,avg(grade) from score group by cno;
mysql> select cno,avg(grade) from score group by cno;
        +-------+------------+
        | cno   | avg(grade) |
        +-------+------------+
        | 3-105 |    85.3333 |
        | 6-166 |    81.6667 |
        | 9-888 |    76.3333 |
        +-------+------------+
        3 rows in set (0.00 sec)
        
 -- 查詢score表中至少有2名學生選修的並以3開頭的平均分數
 -- where、聚合函數、having 在from后面的執行順序：
-- where>聚合函數(sum,min,max,avg,count)>having
 -- having條件 若須引入聚合函數來對group by 結果進行過濾 則只能用having 
 -- like 模糊查詢 類似正則
 -- 分析：先分組 select cno,avg(grade) from score group by cno
 -- 第二步 having count(2)>=2
 -- 第三步 and cno like '3%';
 select cno,avg(grade),count(*) from score group by cno having count(cno)>=2 and cno like '3%';

 注意：
 1、where 后不能跟聚合函數，因為where執行順序大於聚合函數。
2、where 子句的作用是在對查詢結果進行分組前，將不符合where條件的行去掉，即在分組之前過濾數據，條件中不能包含聚組函數，使用where條件顯示特定的行。
3、having 子句的作用是篩選滿足條件的組，即在分組之后過濾數據，條件中經常包含聚組函數，使用having 條件顯示特定的組，也可以使用多個分組標准進行分組。
​
-- 查詢分數大於70，小於90的sno列。
select sno grade from score where 70<grade<90;
select sno grade from score where grade between 70 and 90;
    
-- 查詢所有學生的sname,cno 和grade列
select sname,cno,grade from student as st,score as sc where st.sno=sc.sno;
mysql>  select sname,cno,grade from student as st,score as sc where st.sno=sc.sno;
        +--------+-------+-------+
        | sname  | cno   | grade |
        +--------+-------+-------+
        | 王麗       | 3-105 |    92 |
        | 王麗       | 6-166 |    85 |
        | 王麗       | 9-888 |    86 |
        | 匡yi明     | 3-105 |    88 |
        | 匡yi明     | 6-166 |    79 |
        | 匡yi明     | 9-888 |    75 |
        | 陸君      | 3-105 |    76 |
        | 陸君      | 6-166 |    81 |
        | 陸君      | 9-888 |    68 |
        +--------+-------+-------+
        9 rows in set (0.00 sec)
        
-- 查詢所有學生的sno，cname和grade列 course cname score sno and grade
 select sno,cname,grade from course as c,score as s where c.cno=s.cno;
 mysql> select sno,cname,grade from course as c,score as s where c.cno=s.cno;
    +-----+------------+-------+
    | sno | cname      | grade |
    +-----+------------+-------+
    | 103 | 計算機導論           |    92 |
    | 103 | 數字電路         |    85 |
    | 103 | 高等數學         |    86 |
    | 105 | 計算機導論           |    88 |
    | 105 | 數字電路         |    79 |
    | 105 | 高等數學         |    75 |
    | 106 | 計算機導論           |    76 |
    | 106 | 數字電路         |    81 |
    | 106 | 高等數學         |    68 |
    +-----+------------+-------+
    9 rows in set (0.00 sec)

-- 查詢所有學生的sname，cname和grade列
-- sname--student cname--course grade--score
select sname,cname,grade from student as st,course as c,score as sc where c.cno=sc.cno and st.sno=sc.sno;
mysql> select sname,cname,grade from student as st,course as c,s
 c.cno=sc.cno and st.sno=sc.sno;
    +--------+------------+-------+
    | sname  | cname      | grade |
    +--------+------------+-------+
    | 王麗       | 計算機導論           |    92 |
    | 王麗       | 數字電路         |    85 |
    | 王麗       | 高等數學         |    86 |
    | 匡yi明     | 計算機導論           |    88 |
    | 匡yi明     | 數字電路         |    79 |
    | 匡yi明     | 高等數學         |    75 |
    | 陸君      | 計算機導論           |    76 |
    | 陸君      | 數字電路         |    81 |
    | 陸君      | 高等數學         |    68 |
    +--------+------------+-------+
    9 rows in set (0.00 sec)
​
-- 查詢95031班的學生每門課的平均分數 avg()平均分時
-- in 表示或的關系
-- cla-95031--student表 grade--score表 課程名稱 cname--course
select avg(grade),cno from score where sno in (select sno from student where cla='95031') group by cno;
select cla,avg(grade),cname from student as st,course as co,score as sc where st.sno=sc.sno and co.cno=sc.cno;

-- 查詢選修3-105課程的成績高於106號同學3-105成績的所有同學的記錄
select grade from score where sno='106' and cno='3-105';
select * from score where cno='3-105' and grade>(select grade from score where sno='106' and cno='3-105');
mysql> select * from score where cno='3-105' and grade>(select grade from score
where sno='106' and cno='3-105');
+-----+-------+-------+
| sno | cno   | grade |
+-----+-------+-------+
| 103 | 3-105 |    92 |
| 105 | 3-105 |    88 |
+-----+-------+-------+
2 rows in set (0.00 sec)
​
-- 查詢成績高於學號106課程為3-105的成績的所有記錄
select * from score where grade>(select grade from score where sno='106' and cno='3-105');

-- 查詢學號為108,101的同學同年出生的所有學生的sno，sname和sbirthday列。
-- 只要查年份 year(sbirthday)
select * from student where year(sbirthday) in (select year(sbirthday) from student where sno in (101,103));
​
-- 查詢張旭教師任課的學生成績。
select * from teacher where tname ='張旭';
select cno from course where tno=(select * from teacher where tname ='張旭');

-- 查詢選修某課程的同學人數多於3人的教師姓名
select cno from score group by cno having count(*)>2;
select tname from teacher where tno=(select tno from course where cno=(select cno from score group by cno having count(*)>3));

-- 查詢95033班和95031班的全體學生的記錄
select * from student where cla in ('95033','95031');
​
-- 查詢存在有85分以上成績的課程cno.
select cno from score where grade>85;
​
-- 查詢出計算機系教師所教課程的成績表。
select * from score where cno in (select cno from course where tno in (select tno from teacher where depart="計算機系"));

-- 查詢計算機系和電子工程系不同職稱的教師的tname和prof。
-- union 求並集
select prof from teacher where depart='電子工程系';
select * from teacher where depart='計算機系' and prof not in(select prof from teacher where depart='電子工程系')
union
select * from teacher where depart='電子工程系' and prof not in(select prof from teacher where depart='計算機系');

mysql> select * from teacher where depart='計算機系' and prof not in(select pro
 from teacher where depart='電子工程系')
    ->  union
    ->  select * from teacher where depart='電子工程系' and prof not in(select
rof from teacher where depart='計算機系');
+-----+-------+------+---------------------+------+------------+
| tno | tname | tsex | tbirthday           | prof | depart     |
+-----+-------+------+---------------------+------+------------+
| 825 | 王萍     | 女    | 1972-05-05 00:00:00 | 助教     | 計算機系          |
| 856 | 張旭      | 男     | 1969-03-12 00:00:00 | 講師    | 電子工程系
|
+-----+-------+------+---------------------+------+------------+
2 rows in set (0.00 sec)
​
-- 查詢選修編號為3-105課程且成績至少高於選修編號為3-166的同學的cno，sno和grade,且成績從高到低次序排列。
-- any 大於其中至少一個
select * from score where cno='6-166';
select * from score where cno='3-105';
select * from score where cno='3-105' and grade>any(select grade from score where cno='6-166')
order by grade desc;

-- 查詢選修編號為3-105課程且成績至少高於選修編號為3-166的同學的cno，sno和grade
-- all 表示所有
​
select * from score where cno='6-166';
select * from score where cno='3-105';
select * from score where cno='3-105' and grade>all(select grade from score where cno='6-166');
​
-- 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;
​
-- 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';
​
-- 查詢成績比該課程平均成績低的同學的成績表。
-- 復制表score為表a和表b
select con,avg(grade) from score group by cno;
select * from score a where grade<(select avg(grade) from score b where a.cno = b.cno);
mysql>  select * from score a where grade<(select avg(grade) from score b where
a.cno = b.cno);
+-----+-------+-------+
| sno | cno   | grade |
+-----+-------+-------+
| 105 | 6-166 |    79 |
| 105 | 9-888 |    75 |
| 106 | 3-105 |    76 |
| 106 | 6-166 |    81 |
| 106 | 9-888 |    68 |
+-----+-------+-------+
5 rows in set (0.00 sec)
​
-- 查詢所有任課教師的tname和depart
select tname,depart from teacher where tno in (select tno from course);

-- 查詢至少有倆名男生的班號。
select cla from student where ssex='男' group by cla having count(*)>1;
​
-- 查詢student表中不性王的同學記錄。
select * from student;
select * from student where sname not like '王%';
​
-- 查詢student表中每個學生的姓名和年齡
-- year(now()) 查看當前年份
select sname,year(now())-year(sbirthday) from student;

-- 查詢student表中最大值和最小的birthday的日期值
select max(sbirthday) as '最大值',min(sbirthday) as '最小值' from student;
mysql> select max(sbirthday) as '最大值',min(sbirthday) as '最小值' from student
            ;
            +---------------------+---------------------+
            | 最大值                   | 最小值                  |
            +---------------------+---------------------+
            | 1977-09-01 00:00:00 | 1974-06-03 00:00:00 |
            +---------------------+---------------------+
            1 row in set (0.00 sec)
         
-- 以班號和年齡從大到小的順序查詢studente表中的全部記錄。
select * from student order by cla desc,sbirthday;
​
-- 查詢男教師及其所上的課程
select * from course where tno in (select tno from teacher where tsex='男');

-- 查詢最高分同學的sno,cno,和grade.
select * from score where grade=(select max(grade) from score);
​
-- 查詢和王麗同性別的所有同學的sname
select ssex from student where sname='王麗';
select sname from student where ssex=(select ssex from student where sname='王麗');
​
-- 查詢和王麗同性別並在同班的同學sname
select ssex from student where sname='王麗';
select sname from student where ssex=(select ssex from student where sname='王麗') and cla=(select cla from student where sname='王麗');
​
-- 查詢所有選修計算機導論課程的男同學的成績表。
select * from student where ssex='男';
    select * from course where cname='計算機導論';
    select * from score where cno=(select cno from course where cname='計算機導論') and sno in (select sno from student where ssex='男');
  
-- 假設用如下命令建立了一個grade表
create table gradeq(
low int(3),
    upp int(3),
    gradet char(1)
);
insert into gradeq values(90,100,'A');
insert into gradeq values(80,90,'B');
insert into gradeq values(70,80,'C');
insert into gradeq values(60,70,'D');
insert into gradeq values(50,60,'E');
  -- 先查詢所有學生的sno cno 和 gradet列
  select sno,cno,gradet from score,gradeq where grade between low and upp;
  mysql> select sno,cno,gradet from score,gradeq where grade between low and upp;
+-----+-------+--------+
| sno | cno   | gradet |
+-----+-------+--------+
| 101 | 3-105 | A      |
| 103 | 3-105 | A      |
| 103 | 6-166 | B      |
| 103 | 9-888 | B      |
| 105 | 3-105 | B      |
| 105 | 6-166 | C      |
| 105 | 9-888 | C      |
| 106 | 3-105 | C      |
| 106 | 6-166 | B      |
| 106 | 9-888 | D      |
+-----+-------+--------+
10 rows in set (0.00 sec)

sql 的四種連接查詢
-- 內連接 inner join 或者 join
-- 外連接 
-- 左連接 left join 或者 left outer join
-- 有連接 right join 或者 right outer join 
-- 完全外連接 full 或者 full outer join

創建倆個表
person表 id,name,cardId
create table person(
    id int,
        name varchar(20),
        cardId int
    );
    insert into person values(1,'張三',1);
    insert into person values(2,'李四',3);
    insert into person values(3,'王五',6);
    insert into person values(4,'馬六',9);

card表 id,name
    create table card(
    id int,
        name varchar(20)
    );
    
    insert into card values(1,'飯卡');
    insert into card values(2,'中國卡');
    insert into card values(3,'交通卡');
    insert into card values(4,'招商卡');
    insert into card values(5,'平安卡');
    
-- 並沒有創建外鍵
-- inner join 查詢(內連接) 或者可以使用join
-- 代碼解析：倆張表連接以后使得cardId=id使用inner join 來連接
-- join 左右是我們關聯的表 后跟on 后面的是條件
select * from person inner join card on person.cardId=card.id;
mysql> select * from person inner join card on person.cardId=card.id;
        +------+------+--------+------+--------+
        | id   | name | cardId | id   | name   |
        +------+------+--------+------+--------+
        |    1 | 張三     |      1 |    1 | 飯卡       |
        |    2 | 李四     |      3 |    3 | 交通卡      |
        +------+------+--------+------+--------+
        2 rows in set (0.00 sec)
        
-- left join 外連接（左連接）或者 left outer join
select * from person left join card on person.cardId=card.id;
mysql> select * from person left join card on person.cardId=card.id;
    +------+------+--------+------+--------+
    | id   | name | cardId | id   | name   |
    +------+------+--------+------+--------+
    |    1 | 張三     |      1 |    1 | 飯卡       |
    |    2 | 李四     |      3 |    3 | 交通卡      |
    |    3 | 王五     |      6 | NULL | NULL   |
    |    4 | 馬六     |      9 | NULL | NULL   |
    +------+------+--------+------+--------+
    4 rows in set (0.00 sec)
    -- 左外連接,會把左面的數據全都拿出來，而又變得數據條件相等的拿，不等的補NULL
    
-- right join 外連接(右鏈接) 或者 right outer join
select * from person right join card on person.cardId=card.id;
mysql>  select * from person right join card on person.cardId=card.id;
        +------+------+--------+------+--------+
        | id   | name | cardId | id   | name   |
        +------+------+--------+------+--------+
        |    1 | 張三     |      1 |    1 | 飯卡       |
        | NULL | NULL |   NULL |    2 | 中國卡      |
        |    2 | 李四     |      3 |    3 | 交通卡      |
        | NULL | NULL |   NULL |    4 | 招商卡      |
        | NULL | NULL |   NULL |    5 | 平安卡      |
        +------+------+--------+------+--------+
        5 rows in set (0.00 sec)
       -- 右外連接,會把右面的數據全都拿出來，而又變得數據條件相等的拿，不等的補NULL 
​
-- full join 全外連接 
----------- mysql 不支持 full join 外連接 ---------
select * from person full join card on person.cardId=card.id;
-- 所以mysql如果需要實現全外連接就需要用左連接union有鏈接即可
select * from person right join card on person.cardId=card.id
union
select * from person left join card on person.cardId=card.id;
mysql> select * from person right join card on person.cardId=card.id
    ->  union
   ->  select * from person left join card on person.cardId=card.id;
        +------+------+--------+------+--------+
        | id   | name | cardId | id   | name   |
        +------+------+--------+------+--------+
        |    1 | 張三     |      1 |    1 | 飯卡       |
        | NULL | NULL |   NULL |    2 | 中國卡      |
        |    2 | 李四     |      3 |    3 | 交通卡      |
        | NULL | NULL |   NULL |    4 | 招商卡      |
        | NULL | NULL |   NULL |    5 | 平安卡      |
        |    3 | 王五     |      6 | NULL | NULL   |
        |    4 | 馬六     |      9 | NULL | NULL   |
        +------+------+--------+------+--------+
        7 rows in set (0.00 sec)