數據庫 pymysql

[toc]python

pymysql：python操做mysql

安裝

>: pip3 install pymysql

增刪改查

# 選取操做的模塊 pymysql

# pymysql鏈接數據庫的必要參數：主機、端口、用戶名、密碼、數據庫
# 注：pymysql不能提供建立數據庫的服務，數據庫要提早建立
import pymysql

# 1）創建數據庫鏈接對象 conn
# 2）經過 conn 建立操做sql的 遊標對象
# 3）編寫sql交給 cursor 執行
# 4）若是是查詢，經過 cursor對象 獲取結果
# 5）操做完畢，端口操做與鏈接


# 1）創建數據庫鏈接對象 conn
conn = pymysql.connect(user='root', passwd='root', database='oldboy')
# conn = pymysql.connect(user='root', passwd='root', database='oldboy', autocommit=True)

# 2）經過 conn 建立操做sql的 遊標對象
# 注：遊標不設置參數，查詢的結果就是數據元組，數據沒有標識性
# 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 執行

建立表

# 建立表
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：在建立conn對象時，不設置autocommit，默認開啓事務，增刪改操做不會直接映射到數據庫中，
# 須要執行 conn.commit() 動做
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）若是是查詢，經過 cursor對象 獲取結果
# fetchone() 偏移一條取出，fetchmany(n) 偏移n條取出，fetchall() 偏移剩餘所有
r1 = cursor.fetchone()
print(r1)
r2 = cursor.fetchone()
print(r2)
r3 = cursor.fetchmany(1)
print(r3)
r4 = cursor.fetchall()
print(r4)

# 5）操做完畢，端口操做與鏈接
cursor.close()
conn.close()

遊標操做

import pymysql
from pymysql.cursors import DictCursor

# 1）創建數據庫鏈接對象 conn
conn = pymysql.connect(user='root', passwd='root', db='oldboy')
# 2）經過 conn 建立操做sql的 遊標對象
cursor = conn.cursor(DictCursor)
# 3）編寫sql交給 cursor 執行
sql = 'select * from t1'
# 4）若是是查詢，經過 cursor對象 獲取結果
row = cursor.execute(sql)
if row:
    r1 = cursor.fetchmany(2)
    print(r1)

    # 操做遊標
    # cursor.scroll(0, 'absolute')  # absolute絕對偏移，遊標重置，從頭開始偏移
    cursor.scroll(-2, 'relative')  # relative相對偏移，遊標在當前位置進行左右偏移

    r2 = cursor.fetchone()
    print(r2)

# 5）操做完畢，端口操做與鏈接
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('表已建立')
    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('轉帳執行異常')
    conn.rollback()
else:
    print('轉帳成功')
    conn.commit()
"""

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('轉帳執行異常')
    conn.rollback()
else:
    print('轉帳沒有異常')
    if r1 == 1 and r2 == 1:
        print('轉帳成功')
        conn.commit()
    else:
        conn.rollback()

sql注入

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('表已建立')
    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()



# 用戶登陸
usr = input('usr: ')
pwd = input('pwd: ')

# 本身拼接參數必定有sql注入，將數據的佔位填充交給pymysql

"""
sql = 'select * from user where name="%s" and password="%s"' % (usr, pwd)
row = cursor.execute(sql)
if row:
    print('登陸成功')
else:
    print('登陸失敗')
"""
sql = 'select * from user where name=%s and password=%s'
row = cursor.execute(sql, (usr, pwd))
if row:
    print('登陸成功')
else:
    print('登陸失敗')


# 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"

索引

# 索引就是 鍵 - key

"""
1）鍵 是添加給數據庫表的 字段 的
2）給表建立 鍵 後，該表不只會形參 表結構、表數據，還有 鍵的B+結構圖
3）鍵的結構圖是須要維護的，在數據完成增、刪、改操做時，只要影響到有鍵的字段，結構圖都要維護一次
    因此建立鍵後必定會下降 增、刪、改 的效率
4）鍵能夠極大的加快查詢速度(開發需求中，幾乎業務都和查有關係)
5）創建鍵的方式：主鍵、外鍵、惟一鍵、index
"""

import pymysql
from pymysql.cursors import DictCursor
conn = pymysql.connect(user='root', passwd='root', db='oldboy')
cursor = conn.cursor(DictCursor)

# 建立兩張表
# 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)
# )"""
# cursor.execute(sql2)

# 每一個表插入5000條數據
# 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)