用可空外键连接两个表？

I created two tables below, and FK_TypeID is nullable in this case. I want to write a query returning me the join of two tables.

我在下面创建了两个表，在这种情况下FK_TypeID可以为空。我想写一个查询返回两个表的连接。

if FK_TypeID is NULL for a certain row, the TypeName is also NULL. I am not sure how to go about creating such join statement?

如果某个行的FK_TypeID为NULL，则TypeName也为NULL。我不知道如何创建这样的连接语句？

[Actions]
ActionsID
Date
Message
FK_TypeID //links to the table below

[Type]
TypeID
TypeName

My current statment looks like this and it simply skips NULL FK_TypeID rows

我当前的语句看起来像这样，它只是跳过NULL FK_TypeID行

SELECT        *
FROM            Actions 
INNER JOIN      TypeName ON Actions.FK_TypeID = [Type].TypeID

Help would be greatly appreciated!

非常感谢帮助！

2 个解决方案

#1

You just need to use a LEFT JOIN

你只需要使用LEFT JOIN

SELECT Actions.Date, Actions.Message, Type.TypeName
FROM Actions
    LEFT JOIN Type 
        ON Type.TypeID = Actions.FK_TypeID

If a match to Actions is not found to tie it with Type, then all columns in Type will be NULL.

如果未找到与Actions匹配的类型，则Type中的所有列都将为NULL。

Here is a good graphical visualization of the different types of joins in SQL

这是SQL中不同类型连接的良好图形可视化

#2

Use an OUTER JOIN

使用OUTER JOIN

SELECT Actions.Date, Actions.Message, Type.TypeName 
FROM   Actions LEFT OUTER JOIN 
           Type ON Type.TypeID = Actions.FK_TypeID