python--pymysql模块学习笔记

一：两个对象 connection 与 cursor

       调用connect()方法创建 connection对象：

connection = pymysql.connect(args)

       connection对象方法与属性介绍：

close()                           Send the quit message and close the socket.
commit()                       Commit changes to stable storage.
cursor(cursor=None)   Create a new cursor to execute queries with.
open                             Return True if the connection is open
begin()                          Begin transaction;
ping(reconnect=True)  Check if the server is alive.
rollback()                      Roll back the current transaction.
select_db(db)               Set current db.

show_warnings()          Send the “SHOW WARNINGS” SQL command

       cursor对象是用来与数据库进行交互的；通过connection对象调用cursor()方法创建cursor对象

cursor = connection.cursor()
# cursor = connection.cursor(cursor = pymysql.cursors.DictCursor) 

       cursor对象方法与属性介绍：

close()       Closing a cursor just exhausts all remaining data.
execute(query, args=None)   Execute a query ;Return: Number of affected rows (a int number)
# If args is a list or tuple, %s can be used as a placeholder in the query.
# If args is a dict, %(name)s can be used as a placeholder in the query.

executemany(query, args)    Run several data against one query
fetchall()                               Fetch all the rows
fetchmany(size=None)        Fetch several rows

fetchone()                            Fetch the next row

二：代码与笔记

import pymysql  #导入pymysql模块

connection = pymysql.connect(host='127.0.0.1',
                             user='user',
                             password='pwd',
                             database='db',     # 也有用  db='db' ,是数据库的别名,为了兼容MySQLdb
                             charset='utf8',     # 可选
                             cursorclass=pymysql.cursors.DictCursor,  # 可选，这种cursor会以字典的形式返回查询结果
                             autocommit=True)    # 可选 设置为自动提交；默认autocommit=False

cursor = connection.cursor()    # 产生cursor对象，该对象用来与数据库进行交互

sql = 'insert into t1(name,password) values(%s,%s);'
cursor.execute(sql,('rock','123'))
# connection.commit()  若无设置autocommit=True，则需要在这提交以保存你的修改

sql1 = 'select * from t1;'
rows = cursor.execute(sql1)    # 执行一条查询，返回受影响的行数，而不是查询结果
res = cursor.fetchall()        # 取出所有的查询结果

cursor.close()      # 需先关闭cursor
connection.close()  # 最后要关闭connection


# with connection.cursor() as cursor:   # 采用这种方式最后会自动关闭cursor，所以无需再用cursor.close()
#     sql = 'select * from t1;'
#     rows = cursor.execute(sql)
#     res = cursor.fetchall()

# 选用pymysql.cursors.DictCursor  以字典的形式返回查询结果
# 如 {'name': '程咬铁', 'sex': 'female'}    形式为 {列名：列值，列名：列值}

# 注意：查询结果中的每条记录只能被取一次，所有记录取完了再取就会取空（None 或 空列表）
# fetchone()             从查询结果中取出下一条记录
# fetchmany(size=None)   从查询结果中取出几条记录，放入一个列表中；不设置size，默认取出下一条记录
# fetchall()             从查询结果中取出所有记录，放入一个列表中