Python SQLITE3 UPDATE 给出“无”作为输出

Question

如果之前已经回答了类似的问题，我深表歉意，但我是 SQLITE3 的初学者（一天大），我似乎真的无法理解我在这里做错了什么。

我的表（3列即{A1，A2，W}）：

A1 A2 W
12 67 0
15 01 0

Code:

import sqlite3
import pandas as pd
df = pd.read_csv('/Users/advaitbalaji/Desktop/p.txt', sep = '\t', header = 0)
df.head()
connex = sqlite3.connect('database.db')
cur = connex.cursor()
df.to_sql(name = 'database', con = connex, if_exists = 'replace', index = False)
cur.execute("SELECT Weights FROM database WHERE A1 = 12 AND A2 = 67")
k = cur.fetchone()
print(k)
cur.execute("UPDATE database SET W = W + 1 WHERE A1 = 12 AND 2 = 67")
k = cur.fetchone()
print(k)
connex.commit()


Output:  
 (0,)  
 None

我什至对代码进行了以下更改，但输出保持不变：

cur.execute("SELECT Weights FROM database WHERE A1 = 12 AND A2 = 67")
k = cur.fetchone()
print(k)
cur.execute("UPDATE database SET W = ? WHERE A1 = 12 AND A2 = 67",(k[0]+1,))
k = cur.fetchone()
print(k)
connex.commit()

Output:
 (0,)
 None

我似乎无法弄清楚为什么我的输出不如下：

Desired Output:
(0,)
(1,)

Answer 1

您将游标设置为执行更新，要返回结果元组，您需要让游标再次执行选择查询。如果您在开始时为相同的 select 子句复制相同的条件，它应该会返回预期的结果。

cur.execute("SELECT W FROM database WHERE A1 = 12 AND A2 = 67")
k = cur.fetchone()
print(k)
cur.execute("UPDATE database SET W = ? WHERE A1 = 12 AND A2 = 67",(k[0]+1,))
cur.execute("SELECT W FROM database WHERE A1 = 12 AND A2 = 67")
k = cur.fetchone()
print(k)