Python 操作 MySQL 数据库

利用PyMySQL连接MySQL

连接数据库

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

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

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

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

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。）

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

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

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\')

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

一次性查询所有数据

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\')