Python开发【笔记】：为什么pymysql重连后才能查到新添加的数据

PyMysql操控

问题描述：

　　之前做数据库模块的时候用到了pymysql，测试中发现了一个问题，创建两个程序，select.py从数据库中不断的读取，insert.py在数据库中插入多条数据，但是select.py程序查不到新添加的数据，像是做了缓存一样，查到的数据永远不变；只有重启模块，再次建立连接后，新添加的数据才能被查到；还原当时的代码如下：

查询:

# select.py 不断的进行查询

import pymysql
import time
# Connect to the database
connection = pymysql.connect(host='192.168.1.134',
port=3306,
user='remote',
password='tx_1234abc',
db='Jefrey',
charset='utf8mb4',
cursorclass=pymysql.cursors.DictCursor,
)
while True:
with connection.cursor() as cursor:
# Create a new record
sql = " select * from users WHERE email=%s"
# sql = "INSERT INTO `users` (`email`, `password`) VALUES (%s, %s)"
rows_count = cursor.execute(sql, ('webmaster@python.org'))
result = cursor.fetchall()
print(result)
time.sleep(1)

插入：

# insert.py 进行数据插入

import pymysql.cursors
import time

# Connect to the database
connection = pymysql.connect(host='192.168.1.134',
port=3306,
user='remote',
password='tx_1234abc',
db='Jefrey',
charset='utf8mb4',
# autocommit=True,
cursorclass=pymysql.cursors.DictCursor,)
try:
# execute方法
with connection.cursor() as cursor:
# Create a new record
start = time.time()
sql = "INSERT INTO `users` (`email`, `password`) VALUES (%s, %s)"
for i in range(5):
cursor.execute(sql,('webmaster@python.org','test'))
connection.commit()
time.sleep(1)
finally:
connection.close()

运行30秒，查询输出打印：

()
()
()
()
()

此时数据表中的数据确实是插入进去了：

#首先修改隔离界别
set tx_isolation='serializable';
select @@tx_isolation;
+----------------+
| @@tx_isolation |
+----------------+
| SERIALIZABLE   |
+----------------+

#事务A：开启一个新事务
start transaction;

#事务B：在A没有commit之前，这个交叉事务是不能更改数据的
start transaction;
insert tx values('4','4');
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction
update tx set num=10 where id=1;
ERROR 1205 (HY000): Lock wait timeout exceeded; try restarting transaction

SERIALIZABLE

注：

安全性考虑：Serializable>Repeatable read>Read committed>Read uncommitted
数据库效率：Read uncommitted>Read committed>Repeatable read>Serializable

一般情况下，我们会使用Repeatable read、Read committed mysql数据库默认的数据库隔离级别Repeatable read