为什么MySQL执行返回None？

Question

我试图使用Python的(3.4)MySQL模块在本地MySQL数据库上查询,代码如下:

class databases():

  def externaldatabase(self):

  try:
    c = mysql.connector.connect(host="127.0.0.1", user="user",
                                password="password", database="database")
     if c.is_connected():
           c.autocommit = True
      return(c)
    except:
         return(None)
    d = databases().externaldatabase()
    c = d.cursor() 
    r = c.execute('''select * from tbl_wiki''')
    print(r) 
> Returns: None

据我所知,连接成功,数据库由多行组成,但查询始终返回none类型.

MySQL执行函数返回None的实例是什么？

Answer 1

查询执行没有返回值.

您需要遵循的模式是:

cursor creation;
cursor, execute query;
cursor, *fetch rows*;

或者在python中:

c = d.cursor()

c.execute(query)    # selected rows stored in cursor memory

rows = c.fetchall()    # get all selected rows, as Barmar mentioned
for r in rows:
    print(r)

此外,一些数据库模块允许您使用for ... in模式迭代游标,但三重检查有关mysql.