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    sql语句查询一对一，一对多，多对多

    xiaoxiao2021-04-13  56
    

    //创建用户且置密码，在MySQL中行，但在Oracle中行  ----必须在超级管理员身份下操作 create user hncu identified by '1234'

    DROP DATABASE mydb2; //删除数据库 //查询(显示数据库) SHOW DATABASES; /*用Tab键补全代码，类似MyEclipse中的Alt+/ */

    //创建数据库 并手动指定编码格式 //错，因为根据手册的查询，数据库名应该在 EXISTS后面 CREATE DATABASE hncu IF NOT EXISTS DEFAULT CHARACTER SET 'utf8'; //改正： CREATE DATABASE IF NOT EXISTS hncu DEFAULT CHARACTER SET 'utf8';

    //创建表格 CREATE TABLE stud(   id INT PRIMARY KEY,   sname VARCHAR(30) ,   age INT);    //往数据表中插入数据  INSERT INTO stud VALUES( 1003,'Rose',22 );  SELECT * FROM stud;    USE hncu;  SHOW TABLES;//查询(显示)表格  DESC stud;  //查看数据表student的表结构    SELECT sname,age FROM stud; //只查询(显示)表中的指定列    DELETE FROM stud WHERE age=30; //删除年龄为30的表记录    UPDATE stud SET sname='杰克' WHERE sname='Jack'; //更改数据   ----------------------------------------------------------------------- varchar(20)  ----可变的char数组，类似Java当中的String char(20)   ----固定长度的char数组

    //SQL语言 全部忽略大小写----大小写不敏感

    //更改表结构ALTER TABLE (添加一列) ALTER TABLE stud ADD COLUMN score NUMERIC(4,2); INSERT INTO stud VALUES(1004,'张三',38,60); INSERT INTO stud VALUES(1005,'王三',30,60); INSERT INTO stud VALUES(1006,'王五',30,60); INSERT INTO stud VALUES(1007,'王五六',30,80); SELECT * FROM stud; //※范围查询 //查询年龄在24-26之间的学生信息 //连续区间内的查询 SELECT * FROM stud WHERE age>=24 AND age<27; //用BETWEEN是左右都包含，如下功能是[24,26] SELECT * FROM stud WHERE age BETWEEN 24 AND 26; //离散的多个 SELECT * FROM stud WHERE age=24 OR age=38; SELECT * FROM stud WHERE age IN(24,26,30);

    //※模糊查询LIKE  参数：%(任意匹配), _(匹配一个) //查询姓“王”的学生信息 SELECT * FROM stud WHERE sname LIKE '王%' //查询姓“王”且名为单字的学生信息 SELECT * FROM stud WHERE sname LIKE '王_'; //查询姓“王”且名为双字的学生信息 SELECT * FROM stud WHERE sname LIKE '王__'; //查询姓名中包含“五”字的学生信息 SELECT * FROM stud WHERE sname LIKE '%五%';

    //※范围查询和模糊查询联合 //查询姓名中包含“五”字 且 年龄大于30 的学生信息 SELECT * FROM stud WHERE sname LIKE '%五%' AND age>30;

    //查询 //查询无名英雄学生的信息(VARCHAR) SELECT * FROM stud WHERE sname IS NULL; //查询没有年龄信息的学生 //错：SELECT * FROM stud WHERE age==NULL; SELECT * FROM stud WHERE age IS NULL;

    //创建视图 CREATE VIEW studView AS SELECT * FROM stud WHERE score>=60; SELECT * FROM studview;

    //聚合函数 //统计表格的行数 SELECT COUNT(*) AS TEMPTABLE FROM stud; SELECT COUNT(1) AS TEMPTABLE FROM stud; //统计有年龄值的学生人数 SELECT COUNT(age) AS TEMPTABLE FROM stud; //统计有年龄值且有分数值的学生人数 SELECT COUNT(age) AS TEMPTABLE FROM stud WHERE score IS NOT NULL; //统计平均分且取整(AVG函数只统计非NULL的数据记录) SELECT ROUND(AVG(score)) FROM stud; //这种方式一般不用，因为列名是自动生成的，我们在程序中不好访问 SELECT ROUND(AVG(score)) AS averageScore FROM stud;  //分数求和 SELECT SUM(score) AS ss FROM stud;  //年龄最大值 SELECT MAX(age) AS maxAge FROM stud;

    //WHERE子句 IN子句 //查询年龄最小的那个人的名字 SELECT sname FROM stud WHERE age=(SELECT MIN(age) FROM stud); SELECT sname FROM stud WHERE age IN(SELECT MIN(age) FROM stud);

    //排序 SELECT * FROM stud GROUP BY age ASC; //不重复排序(即年龄相同的，只显示第一个0 SELECT * FROM stud GROUP BY age ASC; //显示出所有年龄段 SELECT * FROM stud ORDER BY age ASC; //普通排序--升序 SELECT * FROM stud ORDER BY age DESC; //普通排序--降序

    SELECT DISTINCT sname,age FROM stud GROUP BY age DESC;

    //EXISTS() 判断括号内的内容是否存在----注意，下面的例子，只要存在年龄为26的学生，就会输出所有数据 SELECT * FROM stud WHERE EXISTS( SELECT * FROM stud WHERE age=26 );

    //演示分组 ALTER TABLE stud ADD COLUMN dept VARCHAR(20); UPDATE stud SET dept='信息学院' WHERE score>=65; UPDATE stud SET dept='通信学院' WHERE score=60; UPDATE stud SET dept='土木学院' WHERE score<60; SELECT * FROM stud;

    //分组计算 //计算信息学院学生的平均分 SELECT AVG(score) FROM stud WHERE dept='信息学院';  //按学院计算平均分 SELECT dept,AVG(score) AS '学院平均分' FROM stud GROUP BY dept;

    //插入记录，当数据不全时，要指定列名 INSERT INTO stud(id,sname,age,score) VALUES(1010,'李小明',25,90);

    ------------------------------------ 数据库编码问题 方法1：可以在MySQL的配置文件如my.ini中指定：   default-character-set = GBK  或   default-character-set = utf8 方法2：在创建数据库时自己指定，如： CREATE DATABASE IF NOT EXISTS hncu DEFAULT CHARACTER SET 'utf8'; ▲相比较而言，对我们来讲，第2种方法更好。一是配置文件是平台，不能随意改，而且通常是由DBA来做的，我们没权设置，甚至MySQL都不在我们的电脑中。二是只要我们自己在创建数据库时自己指定编码，无论平台默认配置的是什么编码，对我们没有影响，一句话不依赖你的平台----可移置及兼容性好。

    SHOW VARIABLES; //查询系统中的所有变量 SHOW VARIABLES WHERE variable_name LIKE 'character%'; //查询系统中所有的编码方面的参数 查询结果： character_set_client utf8  //客户端编码 (不同的客户端显示的可能不一样，如cmd窗口和SQLyong) character_set_connection  utf8  //客户端连接数据库时用的编码 character_set_database gbk  //数据库的默认编码(一般来讲，这是由my.ini配置文件定的。这是没进数据库时的通用编码) character_set_filesystem binary  //这是数据库自己存储数据文件时用的编码，跟我们关系不大 character_set_results utf8  //查询之后的结果集的编码 character_set_server gbk  //MySQL数据库服务器自己的编码  iso8859-1在这里称Latin1 character_set_system  utf8 character_set_dir   MySQL安装目录 \share\charsets

    对我们来讲，为了不出现乱码，必须保证client和connection的编码一致，否则就会乱码。 character_ set_database 数据库的编码必须要能够支持中文，否则输入中文有问题的

    //如何设置指定的编码 set character_set_client=gbk;

    SET character_set_client=gbk; SHOW VARIABLES WHERE variable_name LIKE 'character%'; SELECT * FROM stud;//原来的数据显示正常 INSERT INTO stud VALUES(1011,'城院',20,88,'数计学院'); SELECT * FROM stud;//刚刚插入的那条记录，是乱码 //因为我们这里client是gbk，而connection是utf8，不一致了 SET character_set_connection=gbk;//已经把client和connection设成gbk，一致了 INSERT INTO stud VALUES(1012,'城院2',20,88,'数计学院'); SELECT * FROM stud;//显示刚刚插入的那条记录，还是乱码。因为数据库表stud的编码是utf8，而我们客户端与它的连接都是gbk

    ▲综上，client、connection、我们所访问的数据库的编码  这三者都要一致且应该是支持中文的编码 上面只能保证添加到数据库中的汉字不会出现乱码。 ▲如果读取出来，还要看results、所访问的数据库的编码和我们java代码中的解码是否一致。

    CREATE DATABASE IF NOT EXISTS aaa DEFAULT CHARACTER SET 'utf8'; DROP DATABASE aaa;

    SHOW VARIABLES; //查询系统中的所有变量 SHOW VARIABLES WHERE variable_name LIKE 'character%'; //查询系统中所有的编码方面的参数

    SET character_set_client=gbk; SHOW VARIABLES WHERE variable_name LIKE 'character%'; SELECT * FROM stud; INSERT INTO stud VALUES(1011,'城院',20,88,'数计学院'); SET character_set_connection=gbk; INSERT INTO stud VALUES(1012,'城院2',20,88,'数计学院'); SELECT * FROM stud;

    ※SQL加强 DELETE FROM stud WHERE id>=1011; //统计各个学院的平均分且排序 SELECT dept,AVG(score) FROM stud GROUP BY dept  ORDER BY AVG(score);

    //字符串处理函数 SELECT * FROM stud WHERE sname='AAA'; SELECT * FROM stud WHERE TRIM(sname)='AAA'; SELECT * FROM stud WHERE LTRIM(RTRIM(sname))='AAA';//和上面等价 SELECT * FROM stud;

    SHOW VARIABLES WHERE variable_name LIKE 'character%'; SET character_set_connection=utf8; SET character_set_client=utf8;

    UPDATE stud SET dept='数计学院' WHERE id=1011;

    SELECT LEFT(TRIM(sname),2) FROM stud; //取去掉空格后的左起2个字符 SELECT REVERSE(TRIM(sname)) FROM stud;

    CREATE TABLE person(   id INT,   sname VARCHAR(30) ,   age INT ); ALTER TABLE person ADD CONSTRAINT person_pk PRIMARY KEY(id);//更灵活

    DROP TABLE person; CREATE TABLE person(   id INT PRIMARY KEY,   sname VARCHAR(30) NOT NULL,   age INT ); //用NOT NULL 限制非空输入

    SELECT * FROM TABLES;

    //性别字段: 一般不定义成BOOLEAN型，因为有的数据库不支持，为考虑兼容，通常用CHAR(1) CREATE TABLE a(   id INT UNIQUE,   sname VARCHAR(10),   sex CHAR(1) DEFAULT '0' );

    INSERT INTO a VALUES(1,'Jack');  //错：未指定列名的方式赋值时，必须要给全，默认值不给也不行 INSERT INTO a VALUES(1,'Jack','0');//对 INSERT INTO a(id,sname) VALUES(1,'Tom'); //错：UNIQUE限定该列的值必须唯一(可以为NULL，但最多只能有一个) INSERT INTO a(id,sname) VALUES(2,'Tom'); //对，性别未赋，则用默认 //性能优化：指定列名的方式性能更好！

    //显示性别 (真实值与显示值之间的转换) SELECT * FROM a; SELECT id,sname,(CASE sex WHEN '0' THEN '女' WHEN '1' THEN '男' ELSE 'Null' END) xb FROM a;  SELECT id,sname,(CASE sex WHEN '0' THEN '女' WHEN '1' THEN '男' ELSE 'Null' END) AS xb FROM a;  SELECT id,sname,(CASE WHEN sex='0' THEN '女' WHEN sex='1' THEN '男' ELSE 'Null' END) AS xb FROM a;

    //无关子查询 //需求：具有同龄人的学生 SELECT * FROM stud; SELECT * FROM stud WHERE age IN ( SELECT age FROM stud GROUP BY age HAVING COUNT(age)>=2 ) ORDER BY age DESC; //练练别名 SELECT * FROM stud AS xs WHERE age IN ( SELECT age FROM xs GROUP BY age HAVING COUNT(age)>=2 ) ORDER BY age DESC;

    //需求2：不但具有同龄人，而且年龄大于等于30的学生 //法1 SELECT * FROM stud WHERE age IN ( SELECT age FROM stud GROUP BY age HAVING COUNT(age)>=2 AND age>=30 ) ORDER BY age DESC; //法2 SELECT * FROM stud WHERE age>=30 AND age IN ( SELECT age FROM stud GROUP BY age HAVING COUNT(age)>=2 ) ORDER BY age DESC;

    //固定搭配 SELECT * FROM  +  WHERE  + ORDER BY(要放在最后) GROUP BY + HAVING

    ----------------------------------------- DROP TABLE person;

    SELECT NAME, NAME

    CREATE TABLE person(    id INT,    NAME VARCHAR(10),    sex CHAR(1),    wife INT,    husband INT ); INSERT INTO person VALUES(1,'小花','0',0,3); INSERT INTO person VALUES(2,'玉芬','0',0,4); INSERT INTO person VALUES(3,'张三','1',1,0); INSERT INTO person VALUES(4,'李四','1',2,0); INSERT INTO person VALUES(5,'王五','1',0,0);

    //一对一关系的操作：查出每对夫妻的姓名 CREATE VIEW w AS SELECT * FROM person WHERE sex='0'; CREATE VIEW m AS SELECT * FROM person WHERE sex='1'; //不利用表与表之间的关系 SELECT w.NAME AS 妻子, m.NAME AS 丈夫 FROM w,m WHERE w.husband=m.id AND m.wife=w.id; //现在更先进的方式：利用表间的关系 SELECT w.NAME AS 妻子, m.NAME AS 丈夫 FROM w INNER JOIN m ON w.husband=m.id AND m.wife=w.id;

    SELECT * FROM person;

    //一对多的关系  代码演示 //步骤1：画E-R图 //步骤2:分别建实体表，并给多方的表添加外键约束 CREATE TABLE person2(    id VARCHAR(32) PRIMARY KEY,    pname VARCHAR(30),    sex CHAR(1) ); CREATE TABLE car(    id VARCHAR(32) PRIMARY KEY,    cname VARCHAR(30),    price NUMERIC(10,2),    pid VARCHAR(32),    CONSTRAINT car_fk FOREIGN KEY(pid) REFERENCES person2(id) ); DROP TABLE car;

    //步骤3:为两个表添加测试数据 //实体表1 INSERT INTO person2(id,pname,sex) VALUES('P001','Jack','1'); INSERT INTO person2(id,pname,sex) VALUES('P002','Tom','1'); INSERT INTO person2(id,pname,sex) VALUES('P003','Rose','0'); INSERT INTO person2(id,pname,sex) VALUES('P004','Mary','0'); INSERT INTO person2(id,pname,sex) VALUES('P005','Mike','1'); SELECT * FROM person2;

    实体表2 INSERT INTO car(id,cname,price,pid) VALUES('C001','BMW',123.5,'P001'); INSERT INTO car(id,cname,price,pid) VALUES('C002','Benz',123.5,'P001'); INSERT INTO car(id,cname,price,pid) VALUES('C003','BMW',223.5,'P001');

    INSERT INTO car(id,cname,price,pid) VALUES('C011','BMW',83.5,'P003'); INSERT INTO car(id,cname,price,pid) VALUES('C012','Benz',100,'P003'); INSERT INTO car(id,cname,price,pid) VALUES('C013','Audi',223.5,'P003');

    INSERT INTO car(id,cname,price,pid) VALUES('C021','BMW',88.5,'P004'); INSERT INTO car(id,cname,price,pid) VALUES('C022','QQ',10,'P004');

    INSERT INTO car(id,cname,price,pid) VALUES('C023','Audi',73,'P005'); INSERT INTO car(id,cname,price) VALUES('C033','Audi',1000);

    //该句代码执行错误，因为编号为P006的人在Person2表中不存在，这就是参照完整性 INSERT INTO car(id,cname,price,pid) VALUES('C033','Audi',1000,'P006');

    SELECT * FROM car;

    //查询：哪些人有什么样的车 (用"表名.列名"的形式访问列，如果列名不重复，可以省略表名) //利用一方的主键和“多方”的外键进行关联 SELECT person2.pname,car.cname FROM person2,car WHERE person2.id=car.pid; //查询Jack有什么车 SELECT person2.pname,car.cname FROM person2,car WHERE person2.id=car.pid AND person2.pname='Jack' ; //查询哪些人有两辆以上的车 SELECT person2.pname,COUNT(pname) AS 车数量 FROM person2,car WHERE person2.id=car.pid GROUP BY pname HAVING COUNT(pname)>=2 ORDER BY 车数量; SELECT * FROM person2 WHERE id IN ( SELECT pid FROM car GROUP BY pid HAVING COUNT(pid)>=2 );

    //查询哪些人没有车 SELECT * FROM person2 WHERE id NOT IN( SELECT pid FROM car );

    //用左关联(LEFT JOIN)来查询：哪些人有什么样的车(没车的也是一种情况，要显示) SELECT person2.pname,car.cname,car.price FROM person2 LEFT JOIN car ON person2.id=car.pid ORDER BY person2.id;

    //用内关联(INNER JOIN)来查询：哪些人有什么样的车(没车的不显示) SELECT person2.pname,car.cname,car.price FROM person2 INNER JOIN car ON person2.id=car.pid ORDER BY person2.id;

    //查询每辆车的销售情况(如果有主人就显示，没有则显示NULL) SELECT person2.pname,car.cname,car.price FROM person2 RIGHT JOIN car ON person2.id=car.pid ORDER BY person2.id;

    -------------------------------------------------- DELETE FROM person2 WHERE id='P005';

    CREATE TABLE student(    id VARCHAR(32) PRIMARY KEY,    NAME VARCHAR(30),    age INT ); CREATE TABLE ject(    id VARCHAR(32) PRIMARY KEY,    NAME VARCHAR(30),    price NUMERIC(5,2) );

    CREATE TABLE sj(    studId VARCHAR(32) NOT NULL,    jectId VARCHAR(32) );

    //建立联合主键 ALTER TABLE sj ADD CONSTRAINT sj_pk PRIMARY KEY(studId,jectId); //添加外键约束1(为sj表的studId字段添加外键student(id)约束) ALTER TABLE sj ADD CONSTRAINT sj_fk1 FOREIGN KEY(studId) REFERENCES student(id); //添加外键约束2(为sj表的jectId字段添加外键ject(id)约束) ALTER TABLE sj ADD CONSTRAINT sj_fk2 FOREIGN KEY(jectId) REFERENCES ject(id);

    //添加测试数据 //学生表 INSERT INTO student(id,NAME,age) VALUES('S001','Jack',25); INSERT INTO student(id,NAME,age) VALUES('S002','Tom',24); INSERT INTO student(id,NAME,age) VALUES('S003','张三',23); INSERT INTO student(id,NAME,age) VALUES('S004','李四',24); INSERT INTO student(id,NAME,age) VALUES('S005','Rose',25); SELECT * FROM student;

    //课程表 INSERT INTO ject(id,NAME,price) VALUES('J001','Java',25); INSERT INTO ject(id,NAME,price) VALUES('J002','MySQL',30); INSERT INTO ject(id,NAME,price) VALUES('J003','Oracle',55.9); INSERT INTO ject(id,NAME,price) VALUES('J004','软件工程',20.25); INSERT INTO ject(id,NAME,price) VALUES('J005','WEB开发',125); SELECT * FROM ject;

    //选课表 INSERT INTO sj(studId,jectId) VALUES('S001','J001'); INSERT INTO sj(studId,jectId) VALUES('S001','J002'); INSERT INTO sj(studId,jectId) VALUES('S001','J003'); INSERT INTO sj(studId,jectId) VALUES('S002','J001'); INSERT INTO sj(studId,jectId) VALUES('S002','J003'); INSERT INTO sj(studId,jectId) VALUES('S003','J001'); INSERT INTO sj(studId,jectId) VALUES('S003','J002'); INSERT INTO sj(studId,jectId) VALUES('S004','J003'); INSERT INTO sj(studId,jectId) VALUES('S005','J001'); SELECT * FROM sj;

    应用测试 //查询哪些人选了哪些课 ----要求显示：人名，课程名 //采用的是92标准 SELECT student.name,ject.NAME FROM student,ject,sj WHERE student.id=sj.studId AND sj.jectId=ject.id; //采用96标准 SELECT student.name,ject.NAME FROM student        INNER JOIN sj ON student.id=sj.studId        INNER JOIN ject ON sj.jectId=ject.id;

    //查询哪些人没有选课(左关联) SELECT student.name,ject.NAME FROM student        LEFT JOIN sj ON student.id=sj.studId        LEFT JOIN ject ON sj.jectId=ject.id WHERE ject.NAME IS NULL;

    //查询哪些课没人选(右关联) SELECT student.name,ject.NAME FROM student        RIGHT JOIN sj ON student.id=sj.studId        RIGHT JOIN ject ON sj.jectId=ject.id WHERE student.NAME IS NULL; //左右关联可以相互转换，如把上面的代码用左关联 SELECT student.name,ject.NAME FROM ject        LEFT JOIN sj ON ject.id=sj.jectId        LEFT JOIN student ON sj.studId=student.id WHERE student.NAME IS NULL;

    ※存储过程

    //定义存储过程p1 // “DELIMITER

    ”这句是为了让解析器把“ ”当作结束标志(否则默认是把“;“号当作结束标记),这样存储过程中的语句结束符";"就不会当作过程的结束标记。 DELIMITER CREATEPROCEDUREp1()BEGINSELECT∗FROMstud;INSERTINTOstud(id,sname,age,score,dept)VALUES(1014,′刘三丰′,33,55,′通信学院′);END DELIMITER;   //把结束标记还原回来

    CALL p1();  //调用存储过程p1

    //带参数的存储过程 DELIMITER

    CREATEPROCEDUREp2(INidINT,INnmVARCHAR(30))BEGININSERTINTOstud(id,sname)VALUES(id,nm);END DELIMITER ;

    DROP PROCEDURE p2; CALL p2(1015,'吊丝');

    //有返回值的存储过程----参数与变量问题( @变量名  ，一个@为用户变量，两个@即 @@为全局的系统变量 ) DELIMITER

    CREATEPROCEDUREp3(INidINT,INnmVARCHAR(30),OUTnumINT)BEGININSERTINTOstud(id,sname)VALUES(id,nm);SELECTCOUNT(∗)INTOnumFROMstud;END DELIMITER ;  CALL p3(1016,'无名',@aa); SELECT @aa; //输出变量aa的值

    ※事务处理 START TRANSACTION   DELETE FROM stud WHERE id=1015;   DELETE FROM stud WHERE id=1014;   SELECT * FROM stud;

    ROLLBACK /  COMMIT;

    ◎采用事务的java编程 try{     st.execute("START TRANSACTION;");     st.execute("DELETE FROM stud WHERE id=1015;");     st.execute("DELETE FROM stud WHERE id=1014;");     ....     st.execute(" commit();  "); }catch(Exception e){    rollback(); }

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