python connect to mysql database and read data

python connect to mysql database and read data

1. Install the pymysql package

pip install pymysql

Note:

• MySQLdb only supports python2, pymysql supports python3

2. Connect data

import pymysql 
import pandas as pd
from pandas import DataFrame as df
conn = pymysql.Connect(
    host = 'IP地址', 
    port = 端口号,  
    user = '用户名',  
    passwd = '用户密码', 
    db = '数据库名称', 
    charset = 'utf8'
    )

Note:

• View the local IP address: cmd input: ipconfig, IPv4 address
• The host server address in the pymysql.Connect parameter, this machine can be'localhost'

3. Read the data

(1) Use read_sql to read data

sql = 'select * from testa'
data = pd.read_sql(sql, conn)

(2) Use cursor to read data

sql = 'select * from testa'
cur = conn.cursor()  
try: # 使用异常处理，以防程序无法正常运行
    cur.execute(sql)  
    data = df(cur.fetchall(), columns = [col[0] for col in cur.description])  
except Exception as e:
    conn.rollback()  # 发生错误时回滚
    print('事务处理失败', e)
else:
    # conn.commit()  # 事务提交
    print('事务处理成功', cur.rowcount)
cur.close()

Note:

• The difference between read_sql and cursor cursor:
      read_sql: can only execute query data
      cursor cursor: can execute query, insert, update, delete and other operations

• cur.execute(sql):
      Execute specific database operations

• cur.fetchone():
      get a single piece of data
  cur.fetchmany(3):
      get the first 3
  pieces of data cur.fetchall():
      get all data

• Field names are included in the query results:

    # 法1：
    cur = conn.cursor(cursor = pymysql.cursors.DictCursor)  # 设置成DictCursor，结果包含字段名称
    cur.execute(sql) 
    data = df(cur.fetchall())  
    
    # 法2：
    cur = conn.cursor()
    cur.execute(sql) 
    data = df(cur.fetchall(),columns = [col[0] for col in cur.description]) 
  

• conn.commit():
      This statement is required for operations such as insert, update, and delete; it is not required for querying, creating databases, and data tables

• cur.rowcount:
      Returns the number of operations performed

4. Close the database

conn.close()