python链接数据库

(一) 连接mongodb

from pymongo import MongoClient
import pandas as pd

client = MongoClient() # 链接本机服务可不填网址
collection = client["lianjia"]["houseinfo"]  # 读取数据库lianjia下的houseinfo表
data = list(collection.find()) # 查找表全部内容并转化为列表

# 读取成Series
S = pd.Series(data[0])
print(S)

# 读取成DataFrame
df = pd.DataFrame(data)
print(df.head())

(二) 连接mysql

import pymysql
  import pandas as pd
  
  # 通过python连接数据库，创建数据表
  db = pymysql.connect(host='localhost',
                      user='root',
                      password='123456',
                      db='gddx',
                      port=3306)
  
  # 使用cursor()方法准备游标对象
  cursor = db.cursor()
  
  sql = "select * from EMPLOYEE"
  
  zz = pd.read_sql(sql, db)
  print(zz)
  
  date = pd.DataFrame(zz)
  print(date)
  
  # 关闭数据库
  db.close()

(三) python操作mysql的增删改查

• 创建表

  
  # 通过python连接数据库，创建数据表
  db = pymysql.connect("localhost", "root", "123456", "gddx")
  
  # 使用cursor()方法准备游标对象
  cursor = db.cursor()
  
  # 使用Execute()方法执行SQL查询
  cursor.execute("DROP TABLE IF EXISTS employee")
  
  sql = """CREATE TABLE `employee`(
      `id` int(10) NOT NULL  AUTO_INCREMENT,
      `frist_name` char(20) NOT NULL,
      `last_name` char(20) DEFAULT NULL,
      `age` int(11) DEFAULT NULL,
      `sex` char(1) DEFAULT NULL,
      `income` float DEFAULT NULL,
      PRIMARY KEY (`id`)
      )ENGINE=InnoDB DEFAULT CHARSET=utf8;"""
  
  # 创建表
  cursor.execute(sql)
  
  print("Created table Successfull.")
  
  # 关闭数据库
  db.close()```
  

• 插入数据

  
  # 通过python连接数据库，创建数据表
  db = pymysql.connect("localhost", "root", "123456", "gddx")
  
  # 使用cursor()方法准备游标对象
  cursor = db.cursor()
  
  # 写上插入语句
  sql = """INSERT INTO employee(frist_name,
     last_name, age, sex, income)
     VALUES ('chen', 'sanmi', 24, 'W', 8000)"""
  
  # 尝试折行语句
  try:
      cursor.execute(sql)
      db.commit()
  except:
      db.rollback()
  print (sql)
  print('Yes, Insert Successfull.')
  
  # 关闭数据库
  db.close()```
  
  

• 动态插入数据

  
  # 通过python连接数据库，创建数据表
  db = pymysql.connect("localhost", "root", "123456", "gddx")
  
  # 使用cursor()方法准备游标对象
  cursor = db.cursor()
  
  # 写上插入语句
  sql = "INSERT INTO employee(frist_name, \
     last_name, age, sex, income) \
     VALUES ('%s', '%s', '%d', '%c', '%d' )" % \
     ('wu', 'huarou', 25, 'W', 10000)
  
  # 尝试折行语句
  try:
      cursor.execute(sql)
      db.commit()
  except:
      db.rollback()
  print(sql)
  print('Yes, Insert Successfull.')
  
  # 关闭数据库
  db.close()```
  
  

• 读取数据

  
  # 通过python连接数据库，创建数据表
  db = pymysql.connect("localhost", "root", "123456", "gddx")
  
  # 使用cursor()方法准备游标对象
  cursor = db.cursor()
  
  # 按字典返回
  # cursor = db.cursor(pymysql.cursors.DictCursor)
  
  # 写上插入语句
  sql = "SELECT * FROM employee \
         WHERE income >= %d" % (10000)
  
  # 尝试折行语句
  try:
      cursor.execute(sql)
      # 获取每一行数据
      results = cursor.fetchall()
      for row in results:
          print(row)
          fname = row[1]
          lname = row[2]
          age = row[3]
          sex = row[4]
          income = row[5]
          print("name = %s %s,age = %s,sex = %s,income = %s" % \
                (fname, lname, age, sex, income))
  except:
      import traceback
      traceback.print_exc()
      print ("Error: unable to fetch data")
  
  # 关闭数据库
  db.close()```
  
  

• 更新数据

  
  # 通过python连接数据库，创建数据表
  db = pymysql.connect("localhost", "root", "123456", "gddx")
  
  # 使用cursor()方法准备游标对象
  cursor = db.cursor()
  
  sql = "UPDATE EMPLOYEE SET AGE = AGE - 1 \
                            WHERE SEX = '%c'" % ('M')
  
  # 尝试折行语句
  try:
      cursor.execute(sql)
      db.commit()
  except:
      db.rollback()
  
  # 关闭数据库
  db.close()```
  
  

• 删除数据

  
  # 通过python连接数据库，创建数据表
  db = pymysql.connect("localhost", "root", "123456", "gddx")
  
  # 使用cursor()方法准备游标对象
  cursor = db.cursor()
  
  sql = "DELETE FROM EMPLOYEE WHERE AGE = '%d'" % (25)
  
  # 尝试折行语句
  try:
      cursor.execute(sql)
      db.commit()
  except:
      db.rollback()
  
  # 关闭数据库
  db.close()```