11月21号学习(第19天)

1、将users里面的family_id删除

ALTER TABLE users DROP COLUMN family_id;
将users表内的整个family_id字段全部删除

2、将是家人认识的人全部加入users表详细资料


INSERT INTO users (user_id,user_name,password,age,sex,binrthday)
VALUES(105,'chenpeng',13,37,'n','1976-01-01');

INSERT INTO users (user_id,user_name,password,age,sex,binrthday)
VALUES(106,'chenmihua',14,56,'n','1956-01-01');

INSERT INTO users (user_id,user_name,password,age,sex,binrthday)
VALUES(107,'jianglanying',14,54,'v','1958-01-01');

INSERT INTO users (user_id,user_name,password,age,sex,binrthday)
VALUES(108,'luzhongping',15,52,'n','1960-01-01');

INSERT INTO users (user_id,user_name,password,age,sex,binrthday)
VALUES(109,'jiangxiuying',16,50,'v','1962-01-01');

INSERT INTO users (user_id,user_name,password,age,sex,binrthday)
VALUES(1010,'wanshanfeng',17,49,'n','1963-01-01');

INSERT INTO users (user_id,user_name,password,age,sex,binrthday)
VALUES(1011,'jiangjianying',18,48,'v','1965-01-01');

INSERT INTO users (user_id,user_name,password,age,sex,binrthday)
VALUES(1012,'liuhaixiang',19,47,'n','1967-01-01');

INSERT INTO users (user_id,user_name,password,age,sex,binrthday)
VALUES(1013,'jiangjianlan',19,47,'v','1969-01-01');

INSERT INTO users (user_id,user_name,password,age,sex,binrthday)
VALUES(1014,'xinzhiqiang',20,46,'n','1971-01-01');

INSERT INTO users (user_id,user_name,password,age,sex,binrthday)
VALUES(1015,'jiangyulan',21,46,'v','1971-01-01');

3、将她们所在的家庭全部增加进入familys表内

INSERT INTO familys (family_id,family_name)
VALUES(22,'chenjia');

INSERT INTO familys (family_id,family_name)
VALUES(23,'lujia');

INSERT INTO familys (family_id,family_name)
VALUES(24,'wanjia');

INSERT INTO familys (family_id,family_name)
VALUES(25,'xinjia');

INSERT INTO familys (family_id,family_name)
VALUES(26,'liujia');

4、创建一个第三方表FamilyUser里面有三个数据id users_id family_id把前两章表的id都进来

CREATE TABLE FamilyUser (familyuser_id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,user_id INT,family_id INT);
创建FamilyUser表

INSERT INTO FamilyUser (user_id,family_id)
VALUES(101,24);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(102,25);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(103,26);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(104,23);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(105,23);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(106,23);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(107,21);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(108,23);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(109,21);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(1010,24);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(1011,21);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(1012,26);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(1013,21);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(1014,25);

INSERT INTO FamilyUser (user_id,family_id)
VALUES(1015,21);

5、用多对多的关联查询实现出 用户名ID 用户名 家庭名字

SELECT users.user_id,users.user_name,familys.family_name FROM users LEFT JOIN familyuser ON users.user_id = familyuser.user_id LEFT JOIN familys ON familyuser.family_id = familys.family_id;
通过左连接完成所需要的查询

6、在MYSQL 有多少种字段类型 分别多长 对应java里的类型有多少种写在一张单独博客里

7、明天任务但尽快完成 索引的作用
使用索引可快速访问数据库表中的特定信息。
建立索引的目的是加快对表中记录的查找或排序。 　　为表设置索引要付出代价的：一是增加了数据库的存储空间，二是在插入和修改数据时要花费较多的时间(因为索引也要随之变动)。

就是让复杂的关联查询变快了

ALTER TABLE familyuser ADD INDEX (family_id) ;
创建一个索引

SELECT name_id,family_id FROM familyuser WHERE family_id = 21;
查询的索引我创建了一个family_id的索引那么family_id它在查询时会
出现在索引文件里只有一行就是family_id通过找到对应的21在出现你要显示的信息
索引值它会自动排序的


ALTER TABLE family RENAME TO familys;
修改表名

今天的单词

INDEX below give