一、数据库基本操作

1. 想允许在数据库写中文，可在创建数据库时用下面命令create database zcl charset utf8;

2. 查看students表结构desc students;

3. 查看创建students表结构的语句show create table students;

4. 删除数据库drop database zcl;

5. 创建一个新的字段alter table students add column nal char(64);

PS: 本人是很讨厌上面这种“简单解释+代码”的博客。其实我当时在mysql终端写了很多的实例，不过因为当时电脑运行一个看视频的软件，导致我无法Ctrl+C/V。现在懒了哈哈~~

二、python连接数据库

python3不再支持mysqldb。其替代模块是PyMySQL。本文的例子是在python3.4环境。

1. 安装pymysql模块pip3 install pymysql

2. 连接数据库，插入数据实例import pymysql

#生成实例，连接数据库zcl

conn = pymysql.connect(host='127.0.0.1', user='root', passwd='root', db='zcl')

#生成游标，当前实例所处状态

cur = conn.cursor()

#插入数据

reCount = cur.execute('insert into students(name, sex, age, tel, nal) values(%s, %s, %s, %s, %s)',('Jack','man',25,1351234,"CN"))

reCount = cur.execute('insert into students(name, sex, age, tel, nal) values(%s, %s, %s, %s, %s)',('Mary','female',18,1341234,"USA"))

conn.commit() #实例提交命令

cur.close()

conn.close()

print(reCount)

查看结果:mysql> select* from students;+----+------+-----+-----+-------------+------+

| id | name | sex | age | tel | nal |

+----+------+-----+-----+-------------+------+

| 1 | zcl | man | 22 | 15622341234 | NULL |

| 2 | alex | man | 30 | 15622341235 | NULL |

+----+------+-----+-----+-------------+------+

2 rows in set

3. 获取数据import pymysql

conn = pymysql.connect(host='127.0.0.1', user='root', passwd='root', db='zcl')

cur = conn.cursor()

reCount = cur.execute('select* from students')

res = cur.fetchone() #获取一条数据

res2 = cur.fetchmany(3) #获取3条数据

res3 = cur.fetchall() #获取所有(元组格式)

print(res)

print(res2)

print(res3)

conn.commit()

cur.close()

conn.close()

输出:(1, 'zcl', 'man', 22, '15622341234', None)

((2, 'alex', 'man', 30, '15622341235', None), (5, 'Jack', 'man', 25, '1351234', 'CN'), (6, 'Mary', 'female', 18, '1341234', 'USA'))

()

三、事务回滚

事务回滚是在数据写到数据库前执行的，因此事务回滚conn.rollback()要在实例提交命令conn.commit()之前。只要数据未提交就可以回滚，但回滚后ID却是自增的。请看下面的例子:

插入3条数据(注意事务回滚):import pymysql

#连接数据库zcl

conn=pymysql.connect(host='127.0.0.1', user='root', passwd='root', db='zcl')

#生成游标，当前实例所处状态

cur=conn.cursor()

#插入数据

reCount=cur.execute('insert into students(name, sex, age, tel, nal) values(%s, %s, %s, %s, %s)', ('Jack', 'man', 25, 1351234, "CN"))

reCount=cur.execute('insert into students(name, sex, age, tel, nal) values(%s,%s,%s,%s,%s)', ('Jack2', 'man', 25, 1351234, "CN"))

reCount=cur.execute('insert into students(name, sex, age, tel, nal) values(%s, %s, %s, %s, %s)', ('Mary', 'female', 18, 1341234, "USA"))

conn.rollback() #事务回滚

conn.commit() #实例提交命令

cur.close()

conn.close()

print(reCount)

未执行命令前与执行命令后(包含回滚操作)(注意ID号): 未执行上面代码与执行上面代码的结果是一样的!!因为事务已经回滚，故students表不会增加数据!mysql> select* from students;+----+------+--------+-----+-------------+------+

| id | name | sex | age | tel | nal |

+----+------+--------+-----+-------------+------+

| 1 | zcl | man | 22 | 15622341234 | NULL |

| 2 | alex | man | 30 | 15622341235 | NULL |

| 5 | Jack | man | 25 | 1351234 | CN |

| 6 | Mary | female | 18 | 1341234 | USA |

+----+------+--------+-----+-------------+------+

4 rows in set

执行命令后(不包含回滚操作):只需将上面第11行代码注释。mysql> select* from students;+----+-------+--------+-----+-------------+------+

| id | name | sex | age | tel | nal |

+----+-------+--------+-----+-------------+------+

| 1 | zcl | man | 22 | 15622341234 | NULL |

| 2 | alex | man | 30 | 15622341235 | NULL |

| 5 | Jack | man | 25 | 1351234 | CN |

| 6 | Mary | female | 18 | 1341234 | USA |

| 10 | Jack | man | 25 | 1351234 | CN |

| 11 | Jack2 | man | 25 | 1351234 | CN |

| 12 | Mary | female | 18 | 1341234 | USA |

+----+-------+--------+-----+-------------+------+

7 rows in set

总结：虽然事务回滚了，但ID还是自增了，不会因回滚而取消，但这不影响数据的一致性(底层的原理我不清楚~)

四、批量插入数据import pymysql

#连接数据库zcl

conn = pymysql.connect(host='127.0.0.1', user='root', passwd='root', db='zcl')

#生成游标，当前实例所处状态

cur = conn.cursor()

li = [

("cjy","man",18,1562234,"USA"),

("cjy2","man",18,1562235,"USA"),

("cjy3","man",18,1562235,"USA"),

("cjy4","man",18,1562235,"USA"),

("cjy5","man",18,1562235,"USA"),

]

#插入数据

reCount = cur.executemany('insert into students(name,sex,age,tel,nal) values(%s,%s,%s,%s,%s)', li)

#conn.rollback() #事务回滚

conn.commit() #实例提交命令

cur.close()

conn.close()

print(reCount)

pycharm下输出: 5

mysql终端显示:mysql> select* from students; 　 #插入数据前+----+-------+--------+-----+-------------+------+

| id | name | sex | age | tel | nal |

+----+-------+--------+-----+-------------+------+

| 1 | zcl | man | 22 | 15622341234 | NULL |

| 2 | alex | man | 30 | 15622341235 | NULL |

| 5 | Jack | man | 25 | 1351234 | CN |

| 6 | Mary | female | 18 | 1341234 | USA |

| 10 | Jack | man | 25 | 1351234 | CN |

| 11 | Jack2 | man | 25 | 1351234 | CN |

| 12 | Mary | female | 18 | 1341234 | USA |

+----+-------+--------+-----+-------------+------+

7 rows in set

mysql> mysql> select* from students;　　　#插入数据后+----+-------+--------+-----+-------------+------+

| id | name | sex | age | tel | nal |

+----+-------+--------+-----+-------------+------+

| 1 | zcl | man | 22 | 15622341234 | NULL |

| 2 | alex | man | 30 | 15622341235 | NULL |

| 5 | Jack | man | 25 | 1351234 | CN |

| 6 | Mary | female | 18 | 1341234 | USA |

| 10 | Jack | man | 25 | 1351234 | CN |

| 11 | Jack2 | man | 25 | 1351234 | CN |

| 12 | Mary | female | 18 | 1341234 | USA |

| 13 | cjy | man | 18 | 1562234 | USA |

| 14 | cjy2 | man | 18 | 1562235 | USA |

| 15 | cjy3 | man | 18 | 1562235 | USA |

| 16 | cjy4 | man | 18 | 1562235 | USA |

| 17 | cjy5 | man | 18 | 1562235 | USA |

+----+-------+--------+-----+-------------+------+

12 rows in set

学完的东西要及时总结，有些东西忘记了阿~_~