pymysql模块操作数据库

Posted 2021-01-15

 一、连接数据库登录验证示例 

import pymysql

username = input("username:")
password = input("password:")

conn = pymysql.connect(  # 连接数据库
    user="root",
    password="",
    host="localhost",
    port=3306,  # 端口号是数字类型，不要加引号！！！
    database="TestDB",
    charset="utf8")  # charset="utf8",不要写成 utf-8 ！！！

cursor = conn.cursor()  # 获取输入sql语句的光标对象
sql = "select * from userinfo where username=%s and password=%s"
ret = cursor.execute(sql, (username, password))  # 执行sql语句
# sql = "select * from userinfo where username=%(user)s and password=%(pwd)s"
# ret = cursor.execute(sql, {"user": username, "pwd": password})

if ret:
    print("Connection succeeded")
else:
    print("Connection failed")
cursor.close()  # 关闭光标对象
conn.close()  # 关闭连接

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 二、基本使用 

 2.1 创建数据库 

import pymysql

db_conn = pymysql.connect(
    user="root",
    password="",
    host="localhost",
    port=3306,
    database="TestDB",
    charset="utf8")

cursor = db_conn.cursor()
sql = """create table xx(
        id int auto_increment primary key,
        name char(10) not null unique,
        age int not null
        )engine=innodb default charset=utf8"""
cursor.execute(sql)
cursor.close()
db_conn.close()

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 2.2 查找数据时返回字典格式的数据 

import pymysql

db_conn = pymysql.connect(
    user="root",
    password="",
    host="localhost",
    port=3306,
    database="TestDB",
    charset="utf8")

cursor = db_conn.cursor(pymysql.cursors.DictCursor)
sql = "select * from userinfo"
cursor.execute(sql)
ret = cursor.fetchall()
print(ret)
cursor.close()
db_conn.close()

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如果只是 cursor = conn.cursor() ，没有加上上面那些代码，返回的是元祖格式的数据：

 三、pymysql增删改查操作 

 3.1 增 insert 

①普通版插入数据

import pymysql

db_conn = pymysql.connect(
    user="root",
    password="",
    host="localhost",
    port=3306,
    database="TestDB",
    charset="utf8")

cursor = db_conn.cursor()
sql = "insert into userinfo(username, password) values(%s,%s)"
username = "peter"
password = 123456
cursor.execute(sql,(username,password))
db_conn.commit()  # 提交事务！！！一定要记得写！！！
cursor.close()
db_conn.close()

②插入数据失败回滚

import pymysql

db_conn = pymysql.connect(
    user="root",
    password="",
    host="localhost",
    port=3306,
    database="TestDB",
    charset="utf8")

cursor = db_conn.cursor()
sql = "insert into userinfo(username, password) values(%s,%s)"
username = "peter"
password = 123
try:
    cursor.execute(sql,(username,password))
    db_conn.commit()  # 提交事务
except Exception as e:
    print("Error:%s" % e)
    db_conn.rollback()  # 有异常，回滚事务
finally:
    cursor.close()
    db_conn.close()

因为设计表的时候，用户名（username）设置唯一，且上面已经插入一条用户名为 peter 的用户，所以再次插入相同的用户名将会失败，所以使用了异常处理以及回滚事务。或者当用户名和密码，即使其中一个为空的时候，插入数据也会不成功。

③获取刚插入数据的ID值（关联操作要用到）

import pymysql

db_conn = pymysql.connect(
    user="root",
    password="",
    host="localhost",
    port=3306,
    database="TestDB",
    charset="utf8")

cursor = db_conn.cursor()
sql_cla = "insert into class (name) values(%s)"
sql_stu = "insert into student (name, classid) values(%s,%s)"

try:
    cursor.execute(sql_cla,"跆拳道")
    pre_id = cursor.lastrowid  # 获取刚才插入数据的ID值
    cursor.execute(sql_stu,("女汉子",pre_id))
    db_conn.commit()  # 提交事务
except Exception as e:
    db_conn.rollback()  # 有异常，回滚事务
finally:
    cursor.close()
    db_conn.close()

课程表：

学生表：

可以看到课程表有刚插入的跆拳道课程，同时学生表有一个叫做"女汉子"的学生关联到了相应的课程ID。

④批量插入数据

import pymysql

db_conn = pymysql.connect(
    user="root",
    password="",
    host="localhost",
    port=3306,
    database="TestDB",
    charset="utf8")

cursor = db_conn.cursor()
sql = "insert into student (name, classid) values(%s,%s)"
data = (("A","1"),("B","2"),("C","3"))
try:
    ret = cursor.executemany(sql,data)  # 插入多条数据；ret为受影响的行数
    print(ret)  # 3
    db_conn.commit()  # 提交事务
except Exception as e:
    db_conn.rollback()  # 有异常，回滚事务
finally:
    cursor.close()
    db_conn.close()

 3.2 删 delete 

import pymysql

db_conn = pymysql.connect(
    user="root",
    password="",
    host="localhost",
    port=3306,
    database="TestDB",
    charset="utf8")

cursor = db_conn.cursor()
sql = "delete from student where name=%s"
name = "女汉子"
try:
    cursor.execute(sql,name)
    db_conn.commit()
except Exception as e:
    db_conn.rollback()
finally:
    cursor.close()
    db_conn.close()

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 3.3 改 update 

import pymysql

db_conn = pymysql.connect(
    user="root",
    password="",
    host="localhost",
    port=3306,
    database="TestDB",
    charset="utf8")

cursor = db_conn.cursor()
sql = "update student set name=%s, classid=%s where id=%s"
name = "女汉子"
classid = 3
id = 2
try:
    cursor.execute(sql,(name,classid,id))
    db_conn.commit()
except Exception as e:
    db_conn.rollback()
finally:
    cursor.close()
    db_conn.close()

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 3.4 查 select 

①从查到的结果中取单条数据 fetchone()

import pymysql

db_conn = pymysql.connect(
    user="root",
    password="",
    host="localhost",
    port=3306,
    database="TestDB",
    charset="utf8")

cursor = db_conn.cursor()
sql = "select * from student where id=1"
cursor.execute(sql)
ret1 = cursor.fetchone()  # fetchone只取一条数据
print(ret1)  # (1, \'学生1\', 1)
ret2 = cursor.fetchone()  # 再取数据，取不到不会报错，返回None
print(ret2)  # None
cursor.close()
db_conn.close()

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②从查到的结果中取多条数据 fetchmany()

import pymysql

db_conn = pymysql.connect(
    user="root",
    password="",
    host="localhost",
    port=3306,
    database="TestDB",
    charset="utf8")

cursor = db_conn.cursor()
sql = "select * from student where id<10"
cursor.execute(sql)
ret1 = cursor.fetchone()  # fetchone只取一条数据
print(ret1)  # (1, \'学生1\', 1)
ret2 = cursor.fetchmany(3)
print(ret2)  # ((2, \'学生2\', 1), (3, \'学生3\', 2), (4, \'学生4\', 2))
cursor.close()
db_conn.close()

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③从查到的结果中取全部数据 fetchall()

import pymysql

db_conn = pymysql.connect(
    user="root",
    password="",
    host="localhost",
    port=3306,
    database="TestDB",
    charset="utf8")

cursor = db_conn.cursor()
sql = "select * from student where id<=10"
cursor.execute(sql)
ret1 = cursor.fetchone()  # fetchone只取一条数据
print(ret1)  # (1, \'学生1\', 1)
ret2 = cursor.fetchmany(3)
print(ret2)  # ((2, \'学生2\', 1), (3, \'学生3\', 2), (4, \'学生4\', 2))
ret3 = cursor.fetchall()
print(ret3)  # ((5, \'学生5\', 3), (6, \'学生6\', 3), (7, \'学生7\', 4), (8, \'学生8\', 4), (9, \'学生9\', 5), (10, \'学生10\', 5))
cursor.close()
db_conn.close()

④其他操作

cursor.scroll(3,mode="absolute")  # 相对绝对位置移动光标，写多少就是移到多少
cursor.scroll(2,mode="relative")  # 相对当前光标位置再往后移动多少

绝对位置移动光标取数据示例

import pymysql

db_conn = pymysql.connect(
    user="root",
    password="",
    host="localhost",
    port=3306,
    database="TestDB",
    charset="utf8")

cursor = db_conn.cursor()
sql = "select * from student"

cursor.execute(sql)
cursor.scroll(0,mode="absolute")  # 从0开始取，即表中的ID=1的位置
ret1 = cursor.fetchmany(2)  # 往后取2个数据
print(ret1)  # ((1, \'学生1\', 1), (2, \'学生2\', 1))

cursor.scroll(2,mode="absolute")  # 从2开始取，即表中的ID=3的位置
ret2 = cursor.fetchmany(2)  # 往后取2个数据
print(ret2)  # ((3, \'学生3\', 2), (4, \'学生4\', 2))

cursor.close()
db_conn.close()

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相对当前位置移动光标取数据示例

import pymysql

db_conn = pymysql.connect(
    user="root",
    password="",
    host="localhost",
    port=3306,
    database="TestDB",
    charset="utf8")

cursor = db_conn.cursor()
sql = "select * from student"

cursor.execute(sql)
ret1 = cursor.fetchmany(3)
print(ret1)  # ((1, \'学生1\', 1), (2, \'学生2\', 1), (3, \'学生3\', 2))

cursor.scroll(2,mode="relative")  # 本来光标在ID=3位置的后面，然后相对当前位置往后移动了2位，即光标现在处于ID=5位置的后面
ret2 = cursor.fetchmany(2)  # 往后取2个数据，即取ID=6,7位置的数据
print(ret2)  # ((6, \'学生6\', 3), (7, \'学生7\', 4))

cursor.close()
db_conn.close()

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