python pymysql学习总结

python连接数据库需要使用到pymysql模块

import pymysql

conn = pymysql.connect(host = '127.0.0.1', port = 3306, user = 'root', passwd = 'root', db = 'pymysql')

# 不填写参数的情况下，查询返回的结果为元组形式
# cursor = conn.cursor()
# 返回字典需要添加此参数，cursor=pymysql.cursors.DictCursor
cursor = conn.cursor(cursor=pymysql.cursors.DictCursor)

# 查询数据 
r = cursor.execute('SELECT * FROM user')
# 返回查询到的条目数
print(r)

# 返回第一条数据
res = cursor.fetchone()
print(res)

# 从上一次游标结束的位置继续返回，返回第二条第三条数据
res = cursor.fetchmany(2)
print(res)

# 返回所有数据
res = cursor.fetchall()
print(res)

插入数据，在插入前检查是否已存在该条数据，注意变量放在元组中，更新表需要commit()才会生效

username = 'hello'
passwd = 'world'

r = cursor.execute("SELECT * FROM user WHERE  username = %s", username)
if r == 0:
	cursor.execute('INSERT INTO user(username, passwd) VALUES(%s, %s)', (username, passwd))
	conn.commit()
	print('创建成功')
else:
	print('该用户已存在')

更新数据

username = 'hello'
new_passwd = 'china'

cursor.execute("UPDATE user SET passwd = %s WHERE  username = %s", (new_passwd, username))
conn.commit()

删除数据

username = 'hello' 
cursor.execute("DELETE FROM user WHERE username = %s", username)
conn.commit()