Question

I am running a sql in python which returns multiple number of records (of the order of millions) and somewhere in between I am getting a data of NonType which is causing me issues as :TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'. My sql is:

select col1,col2,col3,col4,col5,col6,col7 from table1 where ....

This sql generates multiple records and I want to find out which record/column has that NoneType data. How can I do that?

Answer 1

如果要在Python级别上解决它，可以迭代结果并使用any()检测行中的任何None值：

for result in cursor.fetchall():
    if any(field is None for field in result):
        print(result)
        break  # break once we meet a row with None value

但是，为什么不在数据库级别解决它？例如，查找任何列具有NULL值的所有行：

select 
    col1,col2,col3,col4,col5,col6,col7 
from 
    table1 
where
    (col1 IS NULL or col2 IS NULL or ...)

Answer 2

None is returned by the mysql adapter whenever a cell in the database contains a NULL. If you want to check the record's column for None you can do it with something like

if foo is None:
    do_something()

Answer 3

我知道这是一个老问题，但作为文档，这里有一个例子

用空字符串 None 替换 ""

我在使用包含 Null 值的 sqlite 数据库时遇到了类似的问题。

non_null = lambda x: "" if x is None else x
list = []
for row in cursor.execute("SELECT * FROM Table"):
    # replace None          
    ls = map(non_null,row)

    # create a new tuple because tuples are read-only
    row1 = tuple(ls)
    list.append(row1)

 print(list)

How to check if a sql returns NonType data in python

3 个答案: