138 Python操做MySQL數據庫

時間 2019-11-20

標籤 python mysql 數據庫欄目 Python 简体版

原文原文鏈接

目錄python

1、數據庫的安裝和鏈接

1.1 pymysql的安裝

pip install pymysqlmysql

1.2 python鏈接數據庫

創建數據庫鏈接對象 conn
經過 conn 建立操做sql的遊標對象
編寫sql交給 cursor 執行
若是是查詢，經過 cursor對象獲取結果
操做完畢，端口操做與鏈接

import pymysql
# 注：pymysql不能提供建立數據庫的服務，數據庫要提早建立


1）創建數據庫鏈接對象 conn
conn = pymysql.connect(user='root', passwd='123', database='oldboy')

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

1.3 更多參數版

1.2.1 更多參數版
import pymysql

conn = pymysql.connect(
        host='localhost', user='root', password="root",
        database='db', port=3306, charset='utf-8',
)

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

2、建立表操做

import pymysql

# 建立數據庫鏈接
conn = pymysql.connect(user='root', passwd='123', database='mydb')

# 使用cursor()方法建立一個遊標對象
coursor = conn.cursor()

# 使用sql語句建立表
sql1 = 'create table t1(id int, x int, y int)'

# 使用遊標對象.excute執行這條語句
cursor.execute(sql1)

# 關閉數據庫鏈接
conn.close()

3、操做數據

3.1 增長數據

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

1.增1條記錄
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()
#####################################cmd 圖解
mysql> select * from t1;
+------+------+------+
| id   | x    | y    |
+------+------+------+
|    1 |   10 |  100 |
|    2 |   20 |  200 |
+------+------+------+

2.增多條記錄
cursor.executemany(sql2, [(3, 30, 300), (4, 40, 400)])
conn.commit()
#####################################cmd 圖解
mysql> select * from t1;
+------+------+------+
| id   | x    | y    |
+------+------+------+
|    1 |   10 |  100 |
|    2 |   20 |  200 |
|    3 |   30 |  300 |
|    4 |   40 |  400 |
+------+------+------+

3.2 刪除操做

1.刪除id爲4的這條記錄
sql3 = 'delete from t1 where id=%s'
cursor.execute(sql3, 4)
conn.commit()

############################### cmd 圖解
mysql> select * from t1;
+------+------+------+
| id   | x    | y    |
+------+------+------+
|    1 |   10 |  100 |
|    2 |   20 |  200 |
|    3 |   30 |  300 |
+------+------+------+

3.3 更新操做

1.刪除id爲2的這條記錄
sql4 = 'update t1 set y=666 where id=2'
cursor.execute(sql4)
conn.commit()
################################ cmd 圖解
mysql> select * from t1;
+------+------+------+
| id   | x    | y    |
+------+------+------+
|    1 |   10 |  100 |
|    2 |   20 |  666 |
|    3 |   30 |  300 |
+------+------+------+

3.4 查詢操做

1.查看t1表裏的全部數據
sql5 = 'select * from t1'
row = cursor.execute(sql5)  # 返回值是受影響的行
print(row)

2.若是是查詢，經過 cursor對象 獲取結果
#1.fetchone() 偏移一條取出
sql5 = 'select * from t1'
row = cursor.execute(sql5)
r1 = cursor.fetchone()
print(r1)
#結果：{'id': 1, 'x': 10, 'y': 100}
r2 = cursor.fetchone()
print(r2)
#結果：{'id': 2, 'x': 20, 'y': 666}

#2.fetchmany(n) 偏移n條取出
r3 = cursor.fetchmany(1)
print(r3)
#結果：[{'id': 3, 'x': 30, 'y': 300}]

#3.fetchall() 偏移剩餘所有
r4 = cursor.fetchall()
print(r4)
#結果：[] 由於後面沒有記錄了，因此取出來是空的列表

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

4、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()

5、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()

6、SQL注入問題

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"