Python 和 MySQL-Connector-Python

Question

注意我在 Windows 操作系统上使用以下版本的 Python:

(venv) C:\>python
    Python 3.6.5 (v3.6.5:f59c0932b4, Mar 28 2018, 16:07:46) [MSC v.1900 32 bit (Intel)] on win32
    Type "help", "copyright", "credits" or "license" for more information.

*运行下面的 Python 脚本，输出显示在其下面的目录中。该脚本的大部分内容是从以下来源使用的:

https://pynative.com/python-mysql-select-query-to-fetch-data/

脚本 1

import mysql.connector
from mysql.connector import Error
try:
    cnx = mysql.connector.connect(user='root', password='coldplay123',
                                  host='localhost',
                                  database='nathan_test_1')

    cursor_1 = cnx.cursor()
    s1="select * from dataframe"
    cursor_1.execute(s1)
    data1 = cursor_1.fetchall()

    print("Total number of dataframes: ", cursor_1.rowcount)

    for i1 in data1:
        print(i1)
    cursor_1.close()

except Error as e1:
    print("Failure to connect ... ", e1)

cnx.close()

脚本 1 的输出

Total number of dataframes:  1
('a', 'b', 'c', 699)

*现在，我只更改脚本 1 中的两行只需将它们注释掉就可以在中间并生成以下输出:

脚本 2

import mysql.connector
from mysql.connector import Error
try:
    cnx = mysql.connector.connect(user='root', password='coldplay123',
                                  host='localhost',
                                  database='nathan_test_1')

    cursor_1 = cnx.cursor()
    #s1="select * from nathan"
    #cursor_1.execute(s1)
    data1 = cursor_1.fetchall()

    print("Total number of dataframes: ", cursor_1.rowcount)

    for i1 in data1:
        print(i1)
    cursor_1.close()

except Error as e1:
    print("Failure to connect ... ", e1)

cnx.close()

脚本 2 的输出

Failure to connect ...  No result set to fetch from.

*很容易看出导致此错误的原因，但为什么却不明白允许“cursor_1”执行给定的 SQL 查询会导致此情况错误？

Answer 1

根据PEP 249 - Python Database API Specification v2.0 , fetchone, fetchmany, fetchall documentation ,

An Error (or subclass) exception is raised if the previous call to .execute*() did not produce any result set or no call was issued yet.

fetch*() 调用后应紧接着 execute 调用。