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2020
09-29

python 数据库查询返回list或tuple实例

MySQLdb默认查询结果都是返回tuple，输出时候不是很方便，必须按照0，1这样读取，无意中在网上找到简单的修改方法，就是传递一个cursors.DictCursor就行。

默认程序：

import MySQLdb
db = MySQLdb.connect(host='localhost', user='root', passwd='123456', db='test')
cur = db.cursor()
cur.execute('select * from user')
rs = cur.fetchall()
print rs
# 返回类似如下
# ((1000L, 0L), (2000L, 0L), (3000L, 0L))

修改后：

import MySQLdb
import MySQLdb.cursors
db = MySQLdb.connect(host='localhost', user='root', passwd='123456', db='test',
           cursorclass=MySQLdb.cursors.DictCursor)
cur = db.cursor()
cur.execute('select * from user')
rs = cur.fetchall()
print rs
# 返回类似如下
# ({'age': 0L, 'num': 1000L}, {'age': 0L, 'num': 2000L}, {'age': 0L, 'num': 3000L})

或者也可以用下面替换connect和cursor部分

db = MySQLdb.connect(host='localhost', user='root', passwd='123456', db='test')
cur = db.cursor(cursorclass=MySQLdb.cursors.DictCursor)

我的实践：

输出为元组类型：

import pymysql
 
db = pymysql.connect("localhost", "root", "123456", "filestore")
cursor = db.cursor()
sql='select * from tablelist where id>%s' %4
#查询方法一
cursor.execute(sql)
result=cursor.fetchall()
print('result',result)
 
sql2='select * from tablelist where id>%s'
values=('4') # 此处为元组类型
#查询方法二
cursor.execute(sql2,values)
result2=cursor.fetchall()
print('result2',result2)
id_list=[]
tablename_list=[]
tabletime_lsit=[]
cursor.execute('select * from tablelist where id>%s',[4,])
result3=cursor.fetchall()
print('type(result3)',type(result3))
#对((6, 'engineeringdata20180901', '1535731200'),)类型数据的提取
for i in range(len(result3)):
  id_list.append(result3[i][0])
  tablename_list.append(result3[i][1])
  tabletime_lsit.append(result3[i][2])
print(id_list)
print(tabletime_lsit)
print(tablename_list)
cursor.close()
db.close()
#输出结果：
result ((6, 'engineeringdata20180901', '1535731200'), (618, 'engineeringdata20180904', '1535990400'))
result2 ((6, 'engineeringdata20180901', '1535731200'), (618, 'engineeringdata20180904', '1535990400'))
type(result3) <class 'tuple'>
[6, 618]
['1535731200', '1535990400']
['engineeringdata20180901', 'engineeringdata20180904']

输出为list类型：

list_id=[]
list_tablename=[]
list_tabletime=[]
list=get_list('select * from tablelist where id>%s',[4])
print('list:',list)
# 对[{'id': 6, 'tablename': 'engineeringdata20180901', 'tabletime': '1535731200'},]类型数据的提取
for i in range(len(list)):
  print(list[i])
  list_id.append(list[i]['id'])
  list_tablename.append(list[i]['tablename'])
  list_tabletime.append(list[i]['tabletime'])
print('list_id:',list_id)
print('list_tabletime:',list_tabletime)
print('list_tablename:',list_tablename)
# 输出结果为：
list: [{'id': 6, 'tablename': 'engineeringdata20180901', 'tabletime': '1535731200'}, {'id': 618, 'tablename': 'engineeringdata20180904', 'tabletime': '1535990400'}]
{'id': 6, 'tablename': 'engineeringdata20180901', 'tabletime': '1535731200'}
{'id': 618, 'tablename': 'engineeringdata20180904', 'tabletime': '1535990400'}
list_id: [6, 618]
list_tabletime: ['1535731200', '1535990400']
list_tablename: ['engineeringdata20180901', 'engineeringdata20180904']

补充知识：python下 将 pymysql 返回的元组数据转换为列表

我就废话不多说了，大家还是直接看代码吧！

from itertools import chain
...
sql="select elems from table"
cursor.execute(sql)
elems = cursor.fetchall()
resultlist = list(chain.from_iterable(elems))
...

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