在 SQLAlchemy 中选择 NULL 值

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);

我想选择所有已知已婚的 没有人，也就是说，包括那些婚姻状态为 NULL 的人。

这是 没有的工作原理

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

当然了

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

问题是我正在从 SQLAlchemy 访问它——

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

翻译过来就是..

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'}

没有有用吗

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

我也不知道

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？

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最佳答案

For SQLAlchemy 0.7.9 and newer Please use the answer from @jsnow. !!!

For SQLAlchemy 0.7.8 and older

(as indicated by @augurar): Because sqlalchemy uses magic methods (operator overloading) to create SQL constructs, it can only handle operator such as != or ==, but is not able to work with is (which is a very valid Python construct).

Therefore, to make it work with sqlalchemy, you should use:

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

, basically replace the is None with == None. In this case your query will be translated properly to the following 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 != ?

See IS NULL in the documentation.

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i ran into a similar problem

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

short answer: - there is not a column operator for IS (NOT) NULL now, but there will be

in the meantime you can use either:

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

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

小开

Since SQLAlchemy 0.7.9 you may use the is_ (or is_not) method of the column.

A filter expression like:

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

will generate the parameterized SQL:

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

小开

An elegant way to write it would be to use is_ and is_not, as shown in the following example:

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

The question is quite old, but for completeness, here the version I prefer for readability:

import sqlalchemy as sa


query.filter(people.marriage_status == sa.null())
query.filter(people.marriage_status != sa.null())

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