# 实现：使用Python实现用户登录，如果用户存在则登录成功（假设该用户已在数据库中）
import pymysql
user = input('请输入用户名：')
pwd = input('请输入密码：')

# 1.连接
conn = pymysql.connect(host='127.0.0.1', port=3306, user='root', password='', db='db8', charset='utf8')

# 2.创建游标
cursor = conn.cursor()

#注意%s需要加引号
sql = "select * from userinfo where username='%s' and pwd='%s'" %(user, pwd)
print(sql)

# 3.执行sql语句
cursor.execute(sql)

result=cursor.execute(sql) #执行sql语句，返回sql查询成功的记录数目
print(result)

# 关闭连接，游标和连接都要关闭
cursor.close()
conn.close()

if result:
  print('登陆成功')
else:
  print('登录失败')

# 原来是我们对sql进行字符串拼接
# sql="select * from userinfo where name='%s' and password='%s'" %(username,pwd)
# print(sql)
# result=cursor.execute(sql)

#改写为（execute帮我们做字符串拼接，我们无需且一定不能再为%s加引号了）
sql="select * from userinfo where name=%s and password=%s" #！！！注意%s需要去掉引号，因为pymysql会自动为我们加上
result=cursor.execute(sql,[user,pwd]) #pymysql模块自动帮我们解决sql注入的问题，只要我们按照pymysql的规矩来。

import pymysql
username = input('请输入用户名：')
pwd = input('请输入密码：')

# 1.连接
conn = pymysql.connect(host='localhost', port=3306, user='root', password='', db='db8', charset='utf8')

# 2.创建游标
cursor = conn.cursor()

# 操作
# 增
# sql = "insert into userinfo(username,pwd) values (%s,%s)"

# effect_row = cursor.execute(sql,(username,pwd))
#同时插入多条数据
#cursor.executemany(sql,[('李四'，'110'),（'王五'，'119'）]) 

# print(effect_row)#

# 改
# sql = "update userinfo set username = %s where id = 2"
# effect_row = cursor.execute(sql,username)
# print(effect_row)

# 删
sql = "delete from userinfo where id = 2"
effect_row = cursor.execute(sql)
print(effect_row)

#一定记得commit
conn.commit()

# 4.关闭游标
cursor.close()

# 5.关闭连接
conn.close()

mysql> select * from userinfo;
+----+----------+-----+
| id | username | pwd |
+----+----------+-----+
| 1 | mjj   | 123 |
| 3 | 张三   | 110 |
| 4 | 李四   | 119 |
+----+----------+-----+
3 rows in set (0.00 sec)

# 1.连接
conn = pymysql.connect(host='localhost', port=3306, user='root', password='', db='db8', charset='utf8')

# 2.创建游标
cursor = conn.cursor()

sql = 'select * from userinfo'
cursor.execute(sql)

# 查询第一行的数据
row = cursor.fetchone()
print(row) # (1, 'mjj', '123')

# 查询第二行数据
row = cursor.fetchone()
print(row) # (3, '张三', '110')

# 4.关闭游标
cursor.close()

# 5.关闭连接
conn.close()

import pymysql

# 1.连接
conn = pymysql.connect(host='localhost', port=3306, user='root', password='', db='db8', charset='utf8')

# 2.创建游标
cursor = conn.cursor()

sql = 'select * from userinfo'
cursor.execute(sql)

# 获取所有的数据
rows = cursor.fetchall()
print(rows)

# 4.关闭游标
cursor.close()

# 5.关闭连接
conn.close()

#运行结果
((1, 'mjj', '123'), (3, '张三', '110'), (4, '李四', '119'))

# 1.Python实现用户登录
# 2.Mysql保存数据

import pymysql

# 1.连接
conn = pymysql.connect(host='localhost', port=3306, user='root', password='', db='db8', charset='utf8')

# 2.创建游标
cursor = conn.cursor(cursor=pymysql.cursors.DictCursor)

sql = 'select * from userinfo'
cursor.execute(sql)

# 查询第一行的数据
row = cursor.fetchone()
print(row) # (1, 'mjj', '123')

# 查询第二行数据
row = cursor.fetchone() # (3, '张三', '110')
print(row)

cursor.scroll(-1,mode='relative') #设置之后，光标相对于当前位置往前移动了一行，所以打印的结果为第二行的数据
row = cursor.fetchone() 
print(row)

cursor.scroll(0,mode='absolute') #设置之后，光标相对于首行没有任何变化，所以打印的结果为第一行数据
row = cursor.fetchone() 
print(row)

# 4.关闭游标
cursor.close()

# 5.关闭连接
conn.close()

#结果如下

{'id': 1, 'username': 'mjj', 'pwd': '123'}
{'id': 3, 'username': '张三', 'pwd': '110'}
{'id': 3, 'username': '张三', 'pwd': '110'}
{'id': 1, 'username': 'mjj', 'pwd': '123'}

import pymysql

# 1.连接
conn = pymysql.connect(host='localhost', port=3306, user='root', password='', db='db8', charset='utf8')


# 2.创建游标
cursor = conn.cursor(cursor=pymysql.cursors.DictCursor)

sql = 'select * from userinfo'
cursor.execute(sql)

# 获取2条数据
rows = cursor.fetchmany(2)
print(rows)

# 4.关闭游标

# rows = cursor.fetchall()
# print(rows)
cursor.close()

# 5.关闭连接
conn.close()

#结果如下：
[{'id': 1, 'username': 'mjj', 'pwd': '123'}, {'id': 3, 'username': '张三', 'pwd': '110'}]