在 Python MySQL 中输出时未定义值？

Question

在先前提出的问题的帮助下，请参阅（), I'm attempting to apply to a MySQL connector script written in python. As seen by @Popeye 's fiddle http://sqlfiddle.com/#!9/997790/25，我现在尝试返回所有行，其中 C 的值为空，但其输出如下所示

import mysql.connector

db = mysql.connector.connect(
     host="localhost",
     port="3307",
     user="root",
     passwd="#",
     database="#"
  )
mycursor = db.cursor()
mycursor.execute("CREATE TABLE trial157 (Name TEXT(13) NULL , A1 TEXT(13) NULL ,  A2 TEXT(13) NULL ,  A3 TEXT(13) NULL ,  A4 TEXT(13) NULL)")


sql = "INSERT INTO trial157(Name, A1, A2, A3, A4) VALUES (%s, %s, %s, %s, %s)"
val = [
  ('Person A', 'C', 'T', 'R', 'S'),
  ('Person B', 'M', 'V', 'R', 'S'),
  ('Person C', 'M', None , 'R', 'C')
]
mycursor.executemany(sql, val)
db.commit()


mycursor.execute("SELECT * From (select name_new, max(case when name = 'PersonA' then A end) as PersonA, max(case when name = 'PersonB' then A end) as PersonB, max(case when name = 'PersonC' then A end) as PersonC from (select name, 'A1' name_new, A1 A from trial157 union all select name, 'A2' name_new, A2 A from trial157 union all select name, 'A3' name_new, A3 A from trial157 union all select name, 'A4' name_new, A4 A from trial157 ) t group by name_new) t where PersonC is null")
myresult = mycursor.fetchall()
for x in myresult:
  print(x)

 - OUTPUT
('A1', None, None, None)                                                                                     
('A2', None, None, None)
('A3', None, None, None)
('A4', None, None, None)
[Finished in 1.2s]

Answer 1

您使用了错误的名称。（在 case 中使用的表达式名称没有 space。您应该按照 val 使用它完全相同）

替换

max(case when name = 'PersonA' then A end) as PersonA

有

max(case when name = 'Person A' then A end) as PersonA

参见name中Person和A之间的space。对 Person B 和 Person C

做同样的事情

在 Python MySQL 中输出时未定义值？

Values not being defined when outputted in Python MySQL?

python

mysql

pysqlite