在 SQLAlchemy 中选择 NULL 值

Question

这是我的 (PostgreSQL) 表 --

test=> create table people (name varchar primary key,
                            marriage_status varchar) ; 

test=> insert into people values ('Ken', 'married');
test=> insert into people values ('May', 'single');
test=> insert into people values ('Joe', NULL);

我想选择所有不已知已婚的人，即包括婚姻状态为 NULL 的人。

这不工作--

test=> select * from people where marriage_status != 'married' ; 
 name | marriage_status 
------+-----------------
 May  | single
(1 row)

当然可以——

test=> select * from people where marriage_status != 'married'
       or marriage_status is NULL ; 
 name | marriage_status 
------+-----------------
 May  | single
 Joe  | 

问题是我从 SQLAlchemy 使用 --

...filter(or_(people.marriage_status!='married',
              people.marriage_status is None))

翻译成--

SELECT people.name as name,
       people.marriage_status as marriage_status
FROM people 
WHERE people.marriage_status != %(status_1)s OR False
sqlalchemy.engine.base.Engine.... {'status_1': 'married'}

而且不有效--

test=> select * from people where marriage_status != 'married'
       or False; 
 name | marriage_status 
------+-----------------
 May  | single
(1 row)

也不--

test=> select * from people where marriage_status != 'married'
       or NULL; 
 name | marriage_status 
------+-----------------
 May  | single
(1 row)

我应该如何通过 SQLAlchemy 选择 NULL 值？

Answer 1

对于 SQLAlchemy 0.7.8 及更早版本

（如@augurar所示）：由于sqlalchemy使用魔术方法（运算符重载）创建SQL构造，所以只能处理@等运算符987654324@ 或 ==，但不能使用 is（这是一个非常有效的 Python 构造）。

因此，要使其与 sqlalchemy 一起使用，您应该使用：

...filter(or_(people.marriage_status!='married', people.marriage_status == None))

，基本上将is None替换为== None。在这种情况下，您的查询将正确转换为以下 SQL：

SELECT people.name AS people_name, people.marriage_status AS people_marriage_status 
FROM people 
WHERE people.marriage_status IS NULL OR people.marriage_status != ?

在documentation 中查看IS NULL。

Answer 2

从 SQLAlchemy 0.7.9 开始，您可以使用列的is_（或is_not）方法。

过滤表达式，如：

filter(or_(people.marriage_status!='married', people.marriage_status.is_(None)))

将生成参数化的 SQL：

WHERE people.marriage_status != %(status_1)s OR people.marriage_status IS NULL

Answer 3

一种优雅的编写方式是使用 is_ 和 is_not，如下例所示：

query.filter(people.student.is_not(None)) 
query.filter(people.student.is_(None)) 

Answer 4

我遇到了类似的问题

https://groups.google.com/forum/?fromgroups#!topic/sqlalchemy/EVpxsNp5Ifg%5B1-25%5D

简短回答： - 现在没有 IS (NOT) NULL 的列运算符，但会有

与此同时，您可以使用：

filter(tablename.is_deleted.op("IS NOT")(True))

filter(coalesce(tablename.is_deleted, False) != True)