我可以在SQLite中创建计算列吗？ [英] Can I create computed columns in SQLite?

问题描述

例如（如果可能）创建一个名为 Car_Model 的表的语法是什么（如果可能），该表具有表的外键Car_Make ，并给 Car_Make 列，该列是存在的 Car_Models 的数量 Car_Make 。

What would be the syntax (if it's possible), for example, to create a table called Car_Model that has a foreign key to a table Car_Make, and give Car_Make a column which is the number of Car_Models that exist of that Car_Make.

（如果这看起来很琐碎或类似家庭作业，那是因为我只是在家玩一些Python试图重现我在工作中遇到的问题。我们在工作中使用MS-SQL。）

(If this seems trivial or homework-like it's because I am just playing with some python at home trying to recreate a problem I was having at work. We use MS-SQL at work.)

推荐答案

更新：从版本开始 3.31.0 （于2020-01-22发行）， SQLite支持计算列，因此以下答案适用于3.31.0之前的版本

Update: As of version 3.31.0 (released on 2020-01-22), SQLite supports computed columns so the answer below applies to versions prior to 3.31.0

SQLite不支持计算列。

SQLite doesn't supported computed columns.

但是，您的问题可以通过相对简单的SQL查询来解决，然后可以创建视图以使其看起来像带有额外计算的表d列。

However your problem can be solved with a relatively simple SQL Query, you can then create a view to make it appear like a table with the extra computed columns.

SELECT Car_Make.Name, Count(*) AS Count 
FROM Car_Make, Car_Model 
WHERE Car_Make.Id = Car_Model.Make 
GROUP BY Car_Make.Name

这应返回类似于以下内容的表

This should return a table similar to the following

Name      Count
----      -----
Nissan    5
Toyota    20
Ford      10

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