Python全栈之学习MySQL(1) Python全栈之学习MySQL(1)

1. mysql约束
2. 外键_联合主键_唯一索引
3. 存储引擎_表关系
总结

1. mysql约束

# ### char varchar (补充)char字符长度255个varchar 字符长度 21845个# ### part1时间类型dateYYYY-MM-DD 年月日 (节假日,纪念日)timeHH:MM:SS时分秒 (体育竞赛,记录时间)yearYYYY年份(历史,酒的年份)datetimeYYYY-MM-DD HH:MM:SS年月日时分秒 (上线时间,下单时间) create table t1(d date, t time , y year , dt datetime); insert into t1 values("2020-11-3","9:19:30","2020","2020-11-3 9:19:30"); insert into t1 values(now(),now(),now(),now()); timestamp YYYYMMDDHHMMSS(时间戳)自动更新时间 (不需要手动写入,自动实现更新记录,[用作记录修改的时间]) create table t2(dt datetime , ts timestamp); insert into t2 values(20201103092530 , 20201103092530); insert into t2 values(null,null); # 区别 timestamp 自动更新时间(以当前时间戳) datetime没有 insert into t2 values(20390102101010 , 20390102101010); error # 超越2038 # ### part2 约束 : 对编辑的数据进行类型的限制,不满足约束条件的报错 unsigned:无符号 not null:不为空 default:默认值 unique:唯一值,加入唯一索引 (索引相当于字典目录,索引的提出是为了加快速度,一味地乱加索引不会提高查询效率) primary key:主键 auto_increment: 自增加一 zerofill:零填充 foreign key:外键# unsigned 无符号 create table t3(id int unsigned); insert into t3 values(-1); error insert into t3 values(4000000000); success # not null:不为空 create table t4(id int not null , name varchar(11)); insert into t4 values(1,"张宇"); insert into t4 values(null,"张宇"); error insert into t4(name) values("李四"); error # default:默认值 create table t5(id int not null, name varchar(11) default "沈思雨" ); insert into t5 values(1,null); insert into t5(id) values(2); create table t5_2(id int not nulldefault "1111" , name varchar(11) default "沈思雨" ); insert into t5_2 values(); # 在values里面不写值,默认使用默认值; # unique:唯一值,加入唯一索引(索引的提出是为了加快速度,一味地乱加索引不会提高查询效率) # 唯一可为null标记成: UNI create table t6(id int unique , name char(10) default "赵万里" ); insert into t6(id) values(1); insert into t6(id) values(1); error insert into t6(id) values(null); insert into t6(id) values(null); # id变成了多个null# primary key:主键 [ 唯一 + 不为null ]PRI 标记数据的唯一特征 """一个表中,只能设置一个字段为一个主键,unique唯一约束可以设置多个""" # 创建主键 create table t7(id int primary key , name varchar(10) default "赵沈阳"); insert into t7(id) values(1); insert into t7(id) values(1); error insert into t7(id) values(null); error # unique + not null => PRI create table t8(id int unique not null ,name varchar(10) default "赵沈阳" ); # primary key/ unique + not null=> 优先把primary key 作为主键; create table t9(id1 int unique not null ,id2 int primary key ); # 一个表只能设置单个字段为一个主键; create table t10(id1 intprimary key,id2 int primary key ); error # auto_increment: 自增加一 (一般配合主键或者unique 使用) create table t11(id int primary key auto_increment , name varchar(255) default "敬文栋"); insert into t11 values(1,"张三"); insert into t11 values(null,"李四"); insert into t11(id) values(null); # 使用默认值或者自增插入数据 insert into t11 values(); # 删除数据 delete from t11; # 删除数据 + 重置id truncate table t11; # zerofill:零填充 (配合int使用,不够5位拿0来填充) create table t12(id int(5) zerofill); insert into t12 values(1234567); insert into t12 values(12);

2. 外键_联合主键_唯一索引

# ### part3"""主键索引 : PRI[primary key]唯一索引 : UNI[unique]普通索引 : MUL[index]"""# 1.联合唯一索引"""unique(字段1,字段2,字段3 ..... )合在一起,该数据不能重复"""# unique + not nullcreate table t1_server(id int , server_name varchar(10)not null , ip varchar(15) not null , port int not null , unique(ip,port) ); insert into t1_server values(1,"阿里","192.168.11.251",3306); insert into t1_server values(1,"阿里","192.168.11.251",80); insert into t1_server values(1,"阿里","192.168.11.252",80); insert into t1_server values(1,"阿里","192.168.11.252",80); error# unique : 有可能出现多个空值的情况要注意; create table t2_server(id int , server_name varchar(10)not null , ip varchar(15) , port int , unique(ip,port) ); insert into t2_server values(1,"腾讯","192.168.11.251",3306); insert into t2_server values(1,"腾讯","192.168.11.251",3306); errorinsert into t2_server values(1,"腾讯",null,null); # 注意点: 允许插入多个空值; +------+-------------+----------------+------+| id| server_name | ip| port |+------+-------------+----------------+------+|1 | 腾讯| 192.168.11.251 | 3306 ||1 | 腾讯| NULL| NULL ||1 | 腾讯| NULL| NULL ||1 | 腾讯| NULL| NULL ||1 | 腾讯| NULL| NULL |+------+-------------+----------------+------+# 2.联合唯一主键create table t3_server(id int ,server_name varchar(10)not null , ip varchar(15) , port int, primary key(ip,port) ); insert into t3_server values(1,"华为","192.168.11.251",3306); insert into t3_server values(1,"华为","192.168.11.251",3307); """总结:primary key(字段1,字段2 ... )联合唯一主键 , 单个字段情况,可以设置一个主键,如果是多个字段只能设置成联合主键,合在一起表达一个主键概念; unique(字段1,字段2 ... )联合唯一索引index(字段1,字段2 ... )联合普通索引"""# 3.foreign key:外键,把多张表通过一个关联字段联合在一起 (该字段可以设置成外键,作用是可以联级更新或者联级删除)"""语法:foreign key(classid) references class1(id)条件:被关联的字段,必须具备唯一属性; """student1:idnameageclassid1wangtongpei5812liuyifeng8513wangwen182class1:id classname 1python322python33# 创建class1create table class1(id int , classname varchar(255)); # 添加唯一索引alter table class1 add unique(id); # 删除索引create table class222(id int unique, classname varchar(255)); alter table class1 drop index id; # 创建student1create table student1(id int primary key auto_increment,name varchar(255),age int,classid int,foreign key(classid) references class1(id)); # 添加数据insert into class1 values(1,"python32"); insert into class1 values(2,"python33"); insert into class1 values(3,"python34"); insert into student1 values(null,"wangtongpei",58,1); insert into student1 values(null,"liuyifeng",85,1); insert into student1 values(null,"wangwen",18,2); # 没有关联的数据可以直接删除delete from class1 where id = 1; # 有关联的数据不能直接删除,要先把关联的数据删掉之后再删除delete from student1 where id = 3; delete from class1 where id = 2; # 联级更新 , 联级删除 ( 谨慎使用 )"""联级删除 on delete cascade联级更新 on update cascade"""# 创建class2create table class2(id int primary key auto_increment, classname varchar(255)); # 创建student2create table student2(id int primary key auto_increment,name varchar(255),age int,classid int,foreign key(classid) references class2(id) on delete cascade on update cascade #区别); # 添加数据insert into class2 values(1,"python32"); insert into class2 values(2,"python33"); insert into class2 values(3,"python34"); insert into student2 values(null,"wangtongpei",58,1); insert into student2 values(null,"liuyifeng",85,1); insert into student2 values(null,"wangwen",18,2); # 联级删除 (把所有关联数据全部删除,谨慎; )delete from class2 where id = 1; # 联级更新 (把所有关联数据全部更新,谨慎; )update class2 set id = 100 where classname="python33# ### part3"""主键索引 : PRI[primary key]唯一索引 : UNI[unique]普通索引 : MUL[index]"""# 1.联合唯一索引 """unique(字段1,字段2,字段3 ..... )合在一起,该数据不能重复""" # unique + not null create table t1_server(id int , server_name varchar(10)not null , ip varchar(15) not null , port int not null , unique(ip,port) ); insert into t1_server values(1,"阿里","192.168.11.251",3306); insert into t1_server values(1,"阿里","192.168.11.251",80); insert into t1_server values(1,"阿里","192.168.11.252",80); insert into t1_server values(1,"阿里","192.168.11.252",80); error # unique : 有可能出现多个空值的情况要注意; create table t2_server(id int , server_name varchar(10)not null , ip varchar(15) , port int , unique(ip,port) ); insert into t2_server values(1,"腾讯","192.168.11.251",3306); insert into t2_server values(1,"腾讯","192.168.11.251",3306); error insert into t2_server values(1,"腾讯",null,null); # 注意点: 允许插入多个空值; +------+-------------+----------------+------+ | id| server_name | ip| port | +------+-------------+----------------+------+ |1 | 腾讯| 192.168.11.251 | 3306 | |1 | 腾讯| NULL| NULL | |1 | 腾讯| NULL| NULL | |1 | 腾讯| NULL| NULL | |1 | 腾讯| NULL| NULL | +------+-------------+----------------+------+ # 2.联合唯一主键 create table t3_server(id int ,server_name varchar(10)not null , ip varchar(15) , port int, primary key(ip,port) ); insert into t3_server values(1,"华为","192.168.11.251",3306); insert into t3_server values(1,"华为","192.168.11.251",3307); """ 总结:primary key(字段1,字段2 ... )联合唯一主键 , 单个字段情况,可以设置一个主键,如果是多个字段只能设置成联合主键,合在一起表达一个主键概念; unique(字段1,字段2 ... )联合唯一索引index(字段1,字段2 ... )联合普通索引 """ # 3.foreign key:外键,把多张表通过一个关联字段联合在一起 (该字段可以设置成外键,作用是可以联级更新或者联级删除) """语法: foreign key(classid) references class1(id)条件: 被关联的字段,必须具备唯一属性; """ student1:idnameageclassid1wangtongpei5812liuyifeng8513wangwen182 class1:id classname 1python322python33 # 创建class1 create table class1(id int , classname varchar(255)); # 添加唯一索引 alter table class1 add unique(id); # 删除索引 create table class222(id int unique, classname varchar(255)); alter table class1 drop index id; # 创建student1 create table student1( id int primary key auto_increment, name varchar(255), age int, classid int, foreign key(classid) references class1(id) ); # 添加数据 insert into class1 values(1,"python32"); insert into class1 values(2,"python33"); insert into class1 values(3,"python34"); insert into student1 values(null,"wangtongpei",58,1); insert into student1 values(null,"liuyifeng",85,1); insert into student1 values(null,"wangwen",18,2); # 没有关联的数据可以直接删除 delete from class1 where id = 1; # 有关联的数据不能直接删除,要先把关联的数据删掉之后再删除 delete from student1 where id = 3; delete from class1 where id = 2; # 联级更新 , 联级删除 ( 谨慎使用 ) """ 联级删除 on delete cascade 联级更新 on update cascade """ # 创建class2 create table class2(id int primary key auto_increment, classname varchar(255)); # 创建student2 create table student2( id int primary key auto_increment, name varchar(255), age int, classid int, foreign key(classid) references class2(id) on delete cascade on update cascade #区别 ); # 添加数据 insert into class2 values(1,"python32"); insert into class2 values(2,"python33"); insert into class2 values(3,"python34"); insert into student2 values(null,"wangtongpei",58,1); insert into student2 values(null,"liuyifeng",85,1); insert into student2 values(null,"wangwen",18,2); # 联级删除 (把所有关联数据全部删除,谨慎; ) delete from class2 where id = 1; # 联级更新 (把所有关联数据全部更新,谨慎; ) update class2 set id = 100 where classname="python33";

【Python全栈之学习MySQL(1)】
3. 存储引擎_表关系

# ### part4 表与表之间的关系(1) 一对一 : id name age sex address guanlianid userid mother father ....(2) 一对多(多对一) : 班级和学生之间的关系一个班级可以对应多个学生,反过来,多个学生对应一个班级; (3) 多对多 : 一个学生可以同时学习多个学科,一个学科同时可以被多个学生学习一本书可以被多个作者共同编写,一个作者可以写多本书xueke (表1)idname1math2english3wuli student (表2)idname1wangwen2wangwei3wangtongpeirelation (关系表3)"""把 xid 和 sid 这两个关联字段设置成外键,关联xueke表里的id(对应的xid) , 关联student表里的id(对应的sid)"""xid sid111213212223# ### part5 存储引擎 : 存储数据的一种结构方式# 概念:表级锁 :只要有一个线程执行修改表中的相关操作,就会上锁,其他线程默认等待; 行级锁 :针对于当前表中的这条记录,这一行进行上锁,其他数据仍然可以被其他线程修改,实现高并发,高可用; 事务处理: 执行sql语句时,必须所有的操作全部成功,才最终提交数据,有一条失败,直接回滚,恢复到先前状态begin: 开启事务commit: 提交数据rollback: 回滚数据MyISAM: 表级锁(5.5版本之前的默认存储引擎)InnoDB: 事务处理,行级锁,外键 (5.5版本之后的默认存储引擎)MEMORY: 把数据放在内存中,临时缓存; BLACKHOLE: anything you write to it disappears一般用于同步主从数据库; (放在主数据库和从数据库之间的一台服务器; 产生binlog日志进行分发，减轻master的压力)"""主数据库: 增删改从数据库: 查询配置: 一主一从 , 一主多从 , 多主多从""""""show engins; # 查看存储引擎show create table memary1; # 查看创建数据库的结构desc + 表名；# 查看表结构"""create table myisam1( id int ) engine=MyISAM; .frm 表结构.MYD 表数据.MYI 表索引create table innodb1( id int ) engine=InnoDB; .frm 表结构.ibd 表数据+表索引create table memory1( id int ) engine=MEMORY; .frm 只有表结构 , 数据存放在内存中create table blackhole( id int ) engine=BLACKHOLE; .frm 只有表结构 , 所有的数据都不会存储; # ### 额外补充# 关于约束的添加和删除# 1 添加/删除约束 not null #alter table 表名 modify 字段名类型 alter table t1 modify id int not null alter table t1 modify id int# 2 添加/删除 unique 唯一索引 # alter table 表名 add unique(id) alter table t1 add unique(id) alter table t1 drop index id# 3 添加/删除 primary key # alter table 表名 add primary key(id); alter table t1 add primary key(id); alter table t1 drop primary key; # 4 添加/删除 foreign key 外键 (先通过desc 表找到外键名字,然后再删) alter table student1 drop foreign key student1_ibfk_1; #删除 alter table student1 add foreign key(classid) references class1(id) #添加