pymysql：python操作mysql

安裝pymysql

>: pip3 install pymysql

增刪改查

# 選取操作的模塊 pymysql

# pymysql連接數(shù)據(jù)庫的必要參數(shù)：主機、端口、用戶名、密碼、數(shù)據(jù)庫

# 注：pymysql不能提供創(chuàng)建數(shù)據(jù)庫的服務，數(shù)據(jù)庫要提前創(chuàng)建

import pymysql

# 1)建立數(shù)據(jù)庫連接對象 conn

# 2)通過 conn 創(chuàng)建操作sql的 游標對象

# 3)編寫sql交給 cursor 執(zhí)行

# 4)如果是查詢，通過 cursor對象 獲取結果

# 5)操作完畢，端口操作與連接

# 1)建立數(shù)據(jù)庫連接對象 conn

conn = pymysql.connect(user='root', passwd='root', database='oldboy')

# conn = pymysql.connect(user='root', passwd='root', database='oldboy', autocommit=True)

# 2)通過 conn 創(chuàng)建操作sql的 游標對象

# 注：游標不設置參數(shù)，查詢的結果就是數(shù)據(jù)元組，數(shù)據(jù)沒有標識性

# 設置pymysql.cursors.DictCursor，查詢的結果是字典，key是表的字段

cursor = conn.cursor(pymysql.cursors.DictCursor)

# 3)編寫sql交給 cursor 執(zhí)行

創(chuàng)建表

# 創(chuàng)建表

sql1 = 'create table t1(id int, x int, y int)'

cursor.execute(sql1)

增

sql2 = 'insert into t1 values(%s, %s, %s)'

# 增1

cursor.execute(sql2, (1, 10, 100))

cursor.execute(sql2, (2, 20, 200))

# 重點：在創(chuàng)建conn對象時，不設置autocommit，默認開啟事務，增刪改操作不會直接映射到數(shù)據(jù)庫中，

# 需要執(zhí)行 conn.commit() 動作

conn.commit()

# 增多

cursor.executemany(sql2, [(3, 30, 300), (4, 40, 400)])

conn.commit()

刪

sql3 = 'delete from t1 where id=%s'

cursor.execute(sql3, 4)

conn.commit()

改

sql4 = 'update t1 set y=666 where id=2'

cursor.execute(sql4)

conn.commit()

查

sql5 = 'select * from t1'

row = cursor.execute(sql5) # 返回值是受影響的行

print(row)

# 4)如果是查詢，通過 cursor對象 獲取結果

# fetchone() 偏移一條取出，fetchmany(n) 偏移n條取出，fetchall() 偏移剩余全部

r1 = cursor.fetchone()

print(r1)

r2 = cursor.fetchone()

print(r2)

r3 = cursor.fetchmany(1)

print(r3)

r4 = cursor.fetchall()

print(r4)

# 5)操作完畢，端口操作與連接

cursor.close()

conn.close()

游標操作

import pymysql

from pymysql.cursors import DictCursor

# 1)建立數(shù)據(jù)庫連接對象 conn

conn = pymysql.connect(user='root', passwd='root', db='oldboy')

# 2)通過 conn 創(chuàng)建操作sql的 游標對象

cursor = conn.cursor(DictCursor)

# 3)編寫sql交給 cursor 執(zhí)行

sql = 'select * from t1'

# 4)如果是查詢，通過 cursor對象 獲取結果

row = cursor.execute(sql)

if row:

r1 = cursor.fetchmany(2)

print(r1)

# 操作游標

# cursor.scroll(0, 'absolute') # absolute絕對偏移，游標重置，從頭開始偏移

cursor.scroll(-2, 'relative') # relative相對偏移，游標在當前位置進行左右偏移

r2 = cursor.fetchone()

print(r2)

# 5)操作完畢，端口操作與連接

cursor.close()

conn.close()

pymysql事務

import pymysql

from pymysql.cursors import DictCursor

conn = pymysql.connect(user='root', passwd='root', db='oldboy')

cursor = conn.cursor(DictCursor)

try:

sql = 'create table t2(id int, name char(4), money int)'

row = cursor.execute(sql)

print(row)

except:

print('表已創(chuàng)建')

pass

# 空表才插入

row = cursor.execute('select * from t2')

if not row:

sql = 'insert into t2 values(%s,%s,%s)'

row = cursor.executemany(sql, [(1, 'tom', 10), (2, 'Bob', 10)])

conn.commit()

# 可能會出現(xiàn)異常的sql

"""

try:

sql1 = 'update t2 set money=money-1 where name="tom"'

cursor.execute(sql1)

sql2 = 'update t2 set moneys=money+1 where name="Bob"'

cursor.execute(sql2)

except:

print('轉賬執(zhí)行異常')

conn.rollback()

else:

print('轉賬成功')

conn.commit()

"""

解決

try:

sql1 = 'update t2 set money=money-1 where name="tom"'

r1 = cursor.execute(sql1)

sql2 = 'update t2 set money=money+1 where name="ruakei"' # 轉入的人不存在

r2 = cursor.execute(sql2)

except:

print('轉賬執(zhí)行異常')

conn.rollback()

else:

print('轉賬沒有異常')

if r1 == 1 and r2 == 1:

print('轉賬成功')

conn.commit()

else:

conn.rollback()

sql注入問題和解決

import pymysql

from pymysql.cursors import DictCursor

conn = pymysql.connect(user='root', passwd='root', db='oldboy')

cursor = conn.cursor(DictCursor)

try:

sql = 'create table user(id int, name char(4), password char(6))'

row = cursor.execute(sql)

print(row)

except:

print('表已創(chuàng)建')

pass

# 空表才插入

row = cursor.execute('select * from user')

if not row:

sql = 'insert into user values(%s,%s,%s)'

row = cursor.executemany(sql, [(1, 'tom', '123'), (2, 'bob', 'abc')])

conn.commit()

# 用戶登錄

usr = input('usr: ')

pwd = input('pwd: ')

# 自己拼接參數(shù)一定有sql注入，將數(shù)據(jù)的占位填充交給pymysql

"""

sql = 'select * from user where name="%s" and password="%s"' % (usr, pwd)

row = cursor.execute(sql)

if row:

print('登錄成功')

else:

print('登錄失敗')

"""

# 知道用戶名時

# 輸入用戶時：

# tom => select * from user where name="tom" and password="%s"

# tom" # => select * from user where name="tom" #" and password="%s"

# 不自定義用戶名時

# " or 1=1 # => select * from user where name="" or 1=1 #" and password="%s"

解決注入問題

sql = 'select * from user where name=%s and password=%s'

row = cursor.execute(sql, (usr, pwd))

if row:

print('登錄成功')

else:

print('登錄失敗')

索引

索引就是 鍵 - key

1)鍵 是添加給數(shù)據(jù)庫表的 字段 的

2)給表創(chuàng)建 鍵 后，該表不僅會形參 表結構、表數(shù)據(jù)，還有 鍵的B+結構圖

3)鍵的結構圖是需要維護的，在數(shù)據(jù)完成增、刪、改操作時，只要影響到有鍵的字段，結構圖都要維護一次

所以創(chuàng)建鍵后一定會降低 增、刪、改 的效率

4)鍵可以極大的加快查詢速度(開發(fā)需求中，幾乎業(yè)務都和查有關系)

5)建立鍵的方式：主鍵、外鍵、唯一鍵、index

import pymysql

from pymysql.cursors import DictCursor

conn = pymysql.connect(user='root', passwd='root', db='oldboy')

cursor = conn.cursor(DictCursor)

# 創(chuàng)建兩張表

# sql1 = """create table a1(

# id int primary key auto_increment,

# x int,

# y int

# )"""

# cursor.execute(sql1)

# sql2 = """create table a2(

# id int primary key auto_increment,

# x int,

# y int,

# index(x)###############索引，對x的索引，增加索引，提高查詢率。

# )"""

# cursor.execute(sql2)

# 每個表插入5000條數(shù)據(jù)

# import random

# for i in range(1, 5001):

# x = i

# y = random.randint(1, 5000)

# cursor.execute('insert into a1(x, y) values(%s, %s)', (x, y))

# cursor.execute('insert into a2(x, y) values(%s, %s)', (x, y))

#

# conn.commit()

import time

# a1的x、a1的id、a2的x

b_time = time.time()

sql = 'select * from a1 where id=4975'

cursor.execute(sql)

e_time = time.time()

print(e_time - b_time)

b_time = time.time()

sql = 'select * from a1 where x=4975'

cursor.execute(sql)

e_time = time.time()

print(e_time - b_time)

b_time = time.time()

sql = 'select * from a2 where x=4975'

cursor.execute(sql)

e_time = time.time()

print(e_time - b_time)

總結

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