Python --数据库操作

目录

1， mysql

1-1， mysql驱动

1-2， 连接mysql

1-3， 执行sql语句

1-4， 数据表操作

1-4-1， 创建数据表

1-4-2， 查询数据表

1-4-3， 修改数据表

1-4-4， 删除数据表

1-5， 修改数据表内容

1-5-1， 插入数据

1-5-2， 查询数据

1-5-3， 获取结果集

1-5-4， 更新数据

1-5-5， 删除数据

1-6， 断开mysql连接

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1， mysql

1-1， mysql驱动

python要连接mysql需要安装mysql驱动

安装mysql的驱动命令：pip install  mysql-connector-python

In [22]: pip install mysql-connector-python
Looking in indexes: http://mirrors.aliyun.com/pypi/simple/
Collecting mysql-connector-python
  Downloading http://mirrors.aliyun.com/pypi/packages/d3/b8/6798a0f91e595c0704a94c1e32a00ca930f77cb8f0f96c7e4dad4f9db1fe/mysql_connector_python-8.1.0-cp311-cp311-win_amd64.whl (10.8 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 10.8/10.8 MB 777.8 kB/s eta 0:00:00
Requirement already satisfied: protobuf<=4.21.12,>=4.21.1 in c:\users\administrator\appdata\local\programs\python\python311\lib\site-packages (from mysql-connector-python) (4.21.12)
Installing collected packages: mysql-connector-python
Successfully installed mysql-connector-python-8.1.0
Note: you may need to restart the kernel to use updated packages.

1-2， 连接mysql

先创建连接对象，才能mysql进行操作，命令如下：

conn = mysql.connector.conect(user=用户名， password=密码， database=数据库名)

# 导入mysql驱动
In [23]: import mysql.connector

# 创建连接
In [24]: conn = mysql.connector.connect(user='xxxx', password='xxxx', database='scott')

1-3， 执行sql语句

要执行sql语句，需要通过"连接"创建游标，在通过游标执行sql语句

cursor = conn.cursor()：创建游标

cursor.execute(sql语句)：执行单挑sql语句

cursor.executemany(sql语句， 参数列表)

1-4， 数据表操作

1-4-1， 创建数据表

# 创建游标
In [27]: cursor = conn.cursor()

# 通过sql语句创建表
In [47]: cursor.execute('''create table user(
    ...: id bigint not null,
    ...: name varchar(20) not null,
    ...: job varchar(20) not null,
    ...: constraint pk_user_table primary key (id));''')

1-4-2， 查询数据表

# 执行sql语句，查询表
In [59]: cursor.execute('show tables;')

# 获取查询结果
In [60]: cursor.fetchall()
Out[60]:
[('bbb',),
 ('bbb_1',),
 ('dept',),
 ('emp',),
 ('salgrade',),
 ('snapshot_table',),
 ('user',)]

1-4-3， 修改数据表

# 增加一列
In [25]: cursor.execute('alter table user add column address varchar(50) not null;')

# 修改address列名为address_1， 数据类型由varchar(50)修改为varchar(100) 
In [29]: cursor.execute('alter table user change column address address_1 varchar(100) not null')

# 查询修改结果
In [30]: cursor.execute('desc user;')

In [31]: cursor.fetchall()
Out[31]:
[('id', b'bigint(20)', 'NO', 'PRI', None, ''),
 ('name', b'varchar(20)', 'NO', '', None, ''),
 ('job', b'varchar(20)', 'NO', '', None, ''),
 ('address_1', b'varchar(100)', 'NO', '', None, '')]

# 删除address_1列
In [33]: cursor.execute('alter table user drop column address_1')

In [34]: cursor.execute('desc user;')

In [35]: cursor.fetchall()
Out[35]:
[('id', b'bigint(20)', 'NO', 'PRI', None, ''),
 ('name', b'varchar(20)', 'NO', '', None, ''),
 ('job', b'varchar(20)', 'NO', '', None, '')]

1-4-4， 删除数据表

In [39]: cursor.fetchall()
Out[39]:
[('bbb',),
 ('bbb_1',),
 ('dept',),
 ('emp',),
 ('salgrade',),
 ('snapshot_table',),
 ('user',),
 ('user_1',)]

# 删除数据表user_1
In [40]: cursor.execute('drop table user_1;')

In [41]: cursor.execute('show tables;')

In [42]: cursor.fetchall()
Out[42]:
[('bbb',),
 ('bbb_1',),
 ('dept',),
 ('emp',),
 ('salgrade',),
 ('snapshot_table',),
 ('user',)]

1-5， 修改数据表内容

1-5-1， 插入数据

# 向数据表user中插入数据
In [69]: cursor.execute('''
    ...: insert into user
    ...: (id, name, job)
    ...: values
    ...: (1, 'aa', 'aa1'),
    ...: (2, 'bb', 'bb1'),
    ...: (3, 'cc', 'cc1')
    ...: ''')

# 获取收影响的行
In [70]: cursor.rowcount
Out[70]: 3

# 更新数据库数据后，需要提交，数据才能保存到数据库中
In [79]: conn.commit()


# 执行单条sql语句
# 注意这里的占位符为%s， sql语句与参数之间用的是逗号
In [160]: cursor.execute('insert into user (id, name, job) values (%s, %s, %s);', (20, 'fdsa', 'fdsaf'))

# 执行多条sql语句， sql语句与参数之间用的是逗号
In [137]: users
Out[137]: [(4, 'ee', 'ee1'), (5, 'ff', 'ff1')]


In [139]: cursor.executemany('''
     ...: insert into user
     ...: (id, name, job)
     ...: values
     ...: (%s, %s, %s);
     ...: ''', users)

1-5-2， 查询数据

执行查询语句后不会立即回显数据，需要通过fetch*()方法来获取结果集

In [71]: cursor.execute('select * from user;')

1-5-3， 获取结果集

获取结果集通过命令：

cursor.fetchone()：获取结果集一条记录

cursor.fetchmany(n)：根据定义值(n)，获取结果集n条记录

cursor.fetchall()：获取所有结果集

# 通过cursor.fetchall()获取整个结果集
In [72]: cursor.fetchall()
Out[72]: [(1, 'aa', 'aa1'), (2, 'bb', 'bb1'), (3, 'cc', 'cc1')]


In [148]: cursor.execute('select * from user;')

# 获取结果集中一条记录
In [149]: cursor.fetchone()
Out[149]: (1, 'aa', 'aa1')

# 获取结果集中3条记录, 数字3,表示获取3条，根据定义的数字来获取结果集的条数
In [150]: cursor.fetchmany(3)
Out[150]: [(2, 'bb', 'bb1'), (3, 'cc', 'cc1'), (4, 'ee', 'ee1')]


# 若结果集没有被获取完时，再次执行sql语句，会报错
# 这时需要通过cursor.fetchall()获取完整结果集后，再执行sql语句
In [151]: cursor.execute('select * from user;')
---------------------------------------------------------------------------
InternalError                             Traceback (most recent call last)
Cell In[151], line 1
----> 1 cursor.execute('select * from user;')

File ~\AppData\Local\Programs\Python\Python311\Lib\site-packages\mysql\connector\cursor_cext.py:303, in CMySQLCursor.execute(self, operation, params, multi)
    301 except (ProgrammingError, ReferenceError) as err:
    302     raise ProgrammingError("Cursor is not connected", 2055) from err
--> 303 self._cnx.handle_unread_result()
    305 stmt = ""
    306 self.reset()

File ~\AppData\Local\Programs\Python\Python311\Lib\site-packages\mysql\connector\connection_cext.py:955, in CMySQLConnection.handle_unread_result(self, prepared)
    953     self.consume_results()
    954 elif unread_result:
--> 955     raise InternalError("Unread result found")

InternalError: Unread result found

# 获取完整结果集后，再次执行sql语句成功
In [154]: cursor.fetchall()
Out[154]: [(5, 'ff', 'ff1')]

In [156]: cursor.execute('select * from user;')

1-5-4， 更新数据

# 更新id=1的name字段的值
In [66]: cursor.execute('update user set name="aadfsa" where id=1;')

# 注意：数据表数据修改后，需要进行提交，结果才会映射到数据库中
In [67]: conn.commit()

# 查询并获取修改结果
In [68]: cursor.execute('select name from user where id=1;')

In [69]: cursor.fetchall()
Out[69]: [('aadfsa',)]

1-5-5， 删除数据

# 删除id = 2的记录
In [73]: cursor.execute('delete from user where id = 2;')

# 删除后需要提交才会影响到数据库
In [74]: conn.commit()

In [75]: cursor.execute("select * from user;")

In [76]: cursor.fetchall()
Out[76]: [(1, 'aadfsa', 'aa1'), (3, 'cc', 'cc1'), (4, 'ee', 'ee1'), (5, 'ff', 'ff1')]

# 删除整张表数据
In [77]: cursor.execute('delete from user;')

In [78]: conn.commit()

In [79]: cursor.execute("select * from user;")

In [80]: cursor.fetchall()
Out[80]: []

1-6， 断开mysql连接

操作完mysql后，需要断开连接

cursor.close()：断开游标

conn.close()：断开连接

In [168]: cursor.close()
Out[168]: True

In [169]: conn.close()