python学习之数据库操作

一、数据库基本操作数据库操作:查看存储引擎: show engines;查看数据库: show databases; 或者show create database oldboy\G创建数据库: create database oldboy default charset=utf8;删除数据库: drop database oldboy;进入数据库:  use oldboy;数据表操作:创建数据表:create table tb_emp1 (    -> id int(11),    -> name varchar(25),    -> deptId int(11),    -> salary float    -> )engine=innodb default charset=utf8;primary key:create table tb_emp2 (                                                                         -> id int(11) primary key,    -> name varchar(25),    -> deptId int(11),    -> salary float    -> )engine=innodb default charset=utf8;    多个primary key:create table tb_emp3 ( id int(11), name varchar(25), deptId int(11), salary float, primary key(name, deptId) )engine=innodb default charset=utf8;   外键约束foreign key:主表:create table tb_dept1 (    -> id int(11) primary key,    -> name varchar(22) not null,    -> location varchar(50)    -> )engine=innodb default charset=utf8;      从表:create table tb_emp5 (    -> id int(11) primary key,    -> name varchar(25),    -> deptId int(11),    -> salary float,    -> constraint fk_emp_dept1 foreign key(deptId) references tb_dept1(id)    -> )engine=innodb default charset=utf8;    非空约束not null:create table tb_emp6 (    -> id int(11) primary key,    -> name varchar(25) not null,    #非空    -> deptId int(11),    -> salary float,    -> constraint fk_emp_dept2 foreign key(deptId) references tb_dept1(id)    -> )engine=innodb default charset=utf8;唯一性约束unique,要求该列唯一，允许为空，但只能有一个值为空:create table tb_dept2 (    -> id int(11) primary key,    -> name varchar(22) unique,    -> location varchar(50)    -> )engine=innodb default charset=utf8;    默认值default:create table tb_emp7 (    -> id int(11) primary key,    -> name varchar(25) not null,    -> deptId int(11) default 1111,    -> salary float,    -> constraint fk_emp_dept3 foreign key(deptId) references tb_dept1(id)    -> )engine=innodb default charset=utf8;    自增主键auto_increment:create table tb_emp8 (    -> id int(11) primary key auto_increment,    -> name varchar(25) not null,    -> deptId int(11),    -> salary float,    -> constraint fk_emp_dept5 foreign key(deptId) references tb_dept1(id)    -> )engine=innodb default charset=utf8;插入tb_emp8三条数据:insert into tb_emp8(name,salary) values('Lucy', 1000),('lura', 1200),('Kevin',1500);id自增查看表结构: desc tb_emp8; 或者show create table tb_emp8\G修改数据表alter修改表名: alter table tb_dept2 rename tb_deptment3;修改字段类型: alter table tb_dept1 modify name varchar(30);修改字段名: alter table tb_dept1 change location loc varchar(50);添加字段: alter table tb_dept1 add managerId int(10);添加有约束条件的字段: alter table tb_dept1 add column1 varchar(12) not null;在某个位置添加字段: alter table tb_dept1 add column2 int(11) first;在某个字段后面添加新字段: alter table tb_dept1 add column3 int(11) after name;删除字段: alter table tb_dept1 drop column2;修改表的存储引擎: alter table tb_deptment3 engine=MyISAM;删除外键约束: alter table tb_emp9 drop foreign key fk_emp_dept;删除数据表: drop table if exists tb_dept2;删除外键关联的主表，需要首先取消外键关联，否则删除主表失败数据类型×××: TINYINT 1个字节  2**8 - 1=255个值×××: smallint 2个字节×××: int 4个字节×××: bigint 8个字节浮点数单精度: float 4个字节双精度: double 8个字节decimal: 不固定，一般用于财务系统日期时间类型year: 1个字节,格式 YYYYtime: 3个字节,格式 HH:MM:SSdate: 3个字节,格式 YYYY-MM-DDdatetime: 8个字节，格式 YYYY-MM-DD HH:MM:SStimestamp: 4个字节，格式YYYY-MM-DD HH:MM:SS字符串类型char(n): 固定长度字符串    #浪费内存，但查询速度快varchar(n): 非固定长度字符串    #节省内存，但查询速度慢text: 存放文本longtext: 存放大数据文本between .. and .. 关键字使用select 4 between 4 and 6, 4 between 4 and 6, 12 between 9 and 10;in, not in 关键字使用select 2 in(1,3,5,'thks'), 'thks' in(1,3,5,'thks');like用来匹配字符串'%': 匹配任何数目的字符'_': 只能匹配一个字符select查询数据create table fruits (    -> f_id char(10) not null,    -> s_id int not null,    -> f_name char(255) not null,    -> f_price decimal(8,2) not null,    -> primary key(f_id)    -> ) engine    -> ) engine=innodb =utf8;    插入字段:insert into fruits(f_id,s_id,f_name,f_price) values    -> ('a1',101,'apple',5.2),    -> ('b1',102,'blackberry',10.2),    -> ('bs1',102,'orange',11.2),    -> ('bs2',105,'melon',8.2),    -> ('t1',102,'banana',10.3),    -> ('t2',102,'grape',5.3),    -> ('o2',103,'coconut',9.2),    -> ('c0',101,'cherry',3.2),    -> ('a2',103,'apricot',2.2),    -> ('l2',104,'lemon',6.4),    -> ('b2',104,'lemon',7.6),    -> ('m1',106,'mango',15.6),    -> ('m2',105,'xbabay',2.6),    -> ('t4',107,'xbababa',3.6),    -> ('m3',105,'xxtt',11.6),    -> ('b5',107,'xxxx',3.6);单表查询:查询表: select f_id,f_name from fruits;查询条件where: select f_id,f_name from fruits where f_price=10.2;    #等号 =select * from fruits where f_price < 10;        #小于select * from fruits where s_id in(101,102) order by f_name (desc);    #in关键字,按f_name排序，desc降序，asc升序select * from fruits where f_price between 2.00 and 10.20;    #between andselect * from fruits where f_name like 'b%';    #like关键字匹配, %匹配任何多个字符select * from fruits where f_name like '_____y';    #_匹配任意一个字符select * from fruits where s_id='101' and f_price >=5;    #and多条件匹配select * from fruits where s_id='101' or s_id=102;    #or多条件匹配order by查询结果排序select * from fruits order by f_name;select * from fruits order by f_price desc;    #desc倒叙排列group by分组select s_id,count(*) as Total from fruits group by s_id; #根据s_id分组,s_id相同的数量select s_id,count(*) as Total from fruits group by s_id having count(f_name) > 1;    #having后面加上查询条件limit限制查询的数量select * from fruits limit 4;    #查询四条select * from fruits limit 4,3;    #索引为4，从第五条开始返回3条inner join 内连接,返回两表中都有的记录create table suppliers (    -> s_id int(11) not null auto_increment primary key,    -> s_name char(50) not null,    -> s_city char(50),    -> s_zip char(10),    -> s_call char(50) not null    -> )engine=innodb default charset=utf8;以下操作是fruits和suppliers关联select suppliers.s_id, s_name, f_name, f_price from fruits inner join suppliers on     -> fruits.s_id = suppliers.s_id;    #on后面是条件查询，left join    返回包括左表中的所有记录和右表连接字段的所有记录select s_name,f_price from fruits left join suppliers on fruits.s_id = suppliers.s_id;子查询:select s_id, f_name from fruits where s_id=(select s1.s_id from suppliers as s1 where s1.s_city='Tianjin');union合并查询结果并去重union all合并查询不去重select s_id ,f_name,f_price from fruits where f_price < 9.0 union all select s_id,f_name,f_price from fruits where s_id in(101,103);

二、pymysql模块操作数据库例子:#!/usr/bin/python# --*-- coding:utf-8 --*--import pymysqlconn = pymysql.Connect(host='127.0.0.1',user='root',password='aixocm',port=3306,database='oldboy',charset='utf8')cursor = conn.cursor()v = cursor.execute('select * from student')print(v)#cursor.fetchone()    #获取一条数据#cursor.fetchmany(2)    #获取多条数据result = cursor.fetchall()    #获取所有数据print(result)cursor.close()conn.close()#!/usr/bin/python# --*-- coding:utf-8 --*--import pymysqlconn = pymysql.Connect(host='127.0.0.1',user='root',password='aixocm',port=3306,database='oldboy',charset='utf8')cursor = conn.cursor()#v = cursor.execute('insert into student(name) values("test")')#print(v)v = cursor.execute('delete from student where sid=7')conn.commit()    #提交事务cursor.close()conn.close()#!/usr/bin/python# --*-- coding:utf-8 --*--import pymysqlnum=8conn = pymysql.Connect(host='127.0.0.1',user='root',password='aixocm',port=3306,database='oldboy',charset='utf8')cursor = conn.cursor()#v = cursor.execute('insert into student(name) values("test")')#print(v)v = cursor.execute('delete from student where sid=%d' %(num))  #防止sql注入conn.commit()cursor.close()conn.close()