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);

我想选择不已知结婚的所有人，即包括那些有NULL_status的人。

不工作 -

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

当然这样做 -

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

问题是我正在使用 -

从SQLAlchemy访问它

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

被翻译成 -

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'}

不工作 -

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

也没有 -

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

如何通过SQLAlchemy选择NULL值？

Answer 1

（由@augurar表示）：因为 sqlalchemy 使用魔术方法（运算符重载）来创建SQL构造，所以它只能处理运算符，例如!=或==，但无法使用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 != ?

请参阅documentation中的IS NULL。

Answer 2

自SQLAlchemy 0.7.9起，您可以使用该列的is_方法。

过滤器表达式如：

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

将生成参数化SQL：

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

Answer 3

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，但是会有

同时你可以使用：

filter（tablename.is_deleted.op（“IS NOT”）（True））

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

在SQLAlchemy中选择NULL值

3 个答案: