Python 操作 MySQL 数据库

利用PyMySQL连接MySQL

连接数据库

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import pymysql
 
# 连接MySQL           MySQL在本地运行      用户名为root         密码为123456    默认端口3306
db = pymysql.connect(host='localhost', user='root', password='123456', port=3306)
 
# cursor()方法获得MySQL的操作游标，利用游标来执行SQL语句，其中执行方法为execute()
cursor = db.cursor()
 
# 获取MySQL的当前版本
cursor.execute('SELECT VERSION()')
 
# fetchone()方法获得第一条数据，即版本号
data = cursor.fetchone()
print('Database version:', data)
 
# 创建一个名为reptile的数据库,默认编码为utf8mb4
cursor.execute("CREATE DATABASE reptile DEFAULT CHARACTER SET utf8mb4")
db.close()
 
 
 
# 运行输出：
Database version: ('8.0.16',)
# 运行生成一个名为reptile的数据库

创建表

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import pymysql
 
db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
cursor = db.cursor()
sql = '''CREATE TABLE
      IF NOT EXISTS students
      (
      id VARCHAR(255) NOT NULL,
      name VARCHAR(255) NOT NULL,
      age INT NOT NULL,
      PRIMARY KEY (id)
      )'''
# 创建一个名为students的数据表，主键为id
cursor.execute(sql)
db.close()
 
# 运行创建一个数据表

插入数据

方式1

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import pymysql
 
id = '20180001'
user = 'Lee Hua'
age = 20
 
# 连接数据库
db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
# 获得MySQL的操作游标
cursor = db.cursor()
sql = '''INSERT INTO students(id, name, age) VALUES(%s %s %s)'''
 
try:
    # 执行
    cursor.execute(sql, (id, user, age))
    # 数据插入、更新、删除操作，都需要用到commit()方法才能生效
    db.commit()
 
except:
    # 调用rollback()执行数据回滚，相当于什么都没有发生过
    db.rollback()
 
db.close()
 
 
# 运行，数据被插入到数据表中

方式2

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import pymysql
 
db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
cursor = db.cursor()
 
 
data = {
    'id': '20180002',
    'user': 'Lao wang',
    'age': 19
}
table_name = 'students'
keys = ', '.join(data.keys())                   # id, user, age
values = ', '.join(['%s'] * len(data))          # ['%s', '%s', ......]   len(data)个'%s'
sql = '''INSERT INTO {table_name}({keys}) VALUES({values})'''.format(table_name=table_name, keys=keys, values=values)
# sql = INSERT INTO students(id, name, age) VALUES(%s %s %s)
 
 
try:
    tuple_ = tuple(data.values())
    if cursor.execute(sql, tuple_):
        print('成功插入数据')
    db.commit()
 
except:
    print('插入数据失败')
    db.rollback()
 
db.close()

更新数据

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import pymysql
 
db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
cursor = db.cursor()
 
sql = 'UPDATA students SET age = %s WHERE name = %s'
try:
    cursor.execute(sql, (25, 'Bob'))
    db.commit()
except:
    db.rollback()
 
db.close()

实现去重（如果数据存在，则更新数据；如果数据不存在，则插入数据。）

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import pymysql
 
db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
cursor = db.cursor()
 
 
data = {
    'id': '20180002',
    'user': 'Lao wang',
    'age': 19
}
table_name = 'students'
keys = ', '.join(data.keys())                               # keys = id, name, age
values = ', '.join(['%s'] * len(data))                      # values = %s, %s, %s
update = ', '.join(
    [" {key} = %s".format(key=key) for key in data]
)                                                           # id = %s, name = %s, age = %s
sql = '''INSERT INTO {table_name}({keys}) VALUES({values}) ON DUPLICATE KEY update'''.format(table_name=table_name, keys=keys, values=values)
# ON DUPLICATE KEY UPDATE 表示：如果主键已经存在，那么就执行更新操作
 
try:
    tuple_ = tuple(data.values())
    if cursor.execute(sql, tuple_):
        print('成功插入数据')
    db.commit()
 
except:
    print('插入数据失败')
    db.rollback()
 
db.close()

删除数据

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import pymysql
 
db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
cursor = db.cursor()
 
table = 'students'
condition = 'age > 20'
sql = 'DELETE FROM {table} WHERE {conditon}'.format(table=table, conditon=condition)
try:
    cursor.execute(sql)
    db.commit()
except:
    db.rollback()
 
db.close()
 
 
# 删除age > 20的数据

查询数据

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import pymysql
 
db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
cursor = db.cursor()
 
sql = 'SELECT * FROM students WHERE age >= 20'
try:
    cursor.execute(sql)
    print('Count:', cursor.rowcount)        # 调用cursor的rowcount属性，获取查询结果的条数
    one = cursor.fetchone()                 # 获取结果的第一条信息
    print('One:', one)
    result = cursor.fetchall()              # 获取结果的所有数据
    print('Result:', result)
    print('Result Type:', type(result))
    for row in result:
        print(row)
except:
    print('Error')

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# 输出：
Count: 0
One: None
Result: ()
Result Type: <class 'tuple'>

一次性查询所有数据

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import pymysql
 
db = pymysql.connect(host='localhost', user='用户名', password='密码', port=3306, db='reptile')
cursor = db.cursor()
 
sql = 'SELECT * FROM students WHERE age >= 20'
try:
    cursor.execute(sql)
    print('Count:', cursor.rowcount)        # 调用cursor的rowcount属性，获取查询结果的条数
    row = cursor.fetchone()                 # 获取结果的第一条数据
    while row:
        print('Row:', row)
        row = cursor.fetchone()
except:
    print('Error')