如何使用表之间的连接？ [英] How to use connections between tables?

问题描述

例如，我的表帐户， id ，表会话 with account_id 。字段已连接。那么它的可用性是什么？



我尝试过：



要谷歌并在此处找到它。

解决方案

这些列用于将表及其实体链接在一起。给你一个特定的场景，只需考虑以下内容，

账户
 id |名字| ... 
 1 | ABCD | ... 
 2 | EFGH | ... 
 
会话
 id | account_id | ... 
 1 | 1 | ... 
 2 | 43 | ... 
 3 | 3 | ... 
 4 | 1 | ... 
 5 | 2 | ... 

例如，在您想要显示从两个表中链接到特定帐户的所有会话的状态中，您将使用来自帐户的ID和Account_Id从Sessions表到 JOIN 他们在一起。在SQL JOIN中，您可以根据以下标准指定 JOIN 的记录 - 列。



因此，得到这样的东西，

 Account.id | Sessions.id |名字| ... 
 1 | 1 | ABCD | ... 
 1 | 4 | ABCD | ... 

那么进一步的东西是你自己使用数据的逻辑，怎么样？这一切都取决于你，基本上这是在已经规范化的表上完成的。您从表中删除了一些常见的异常，并删除了一些数据冗余。该步骤有时会导致超过1,2或甚至3个表。因此，获取数据需要您加入表格。这些列 - account.id ， sessions.account_id - 充当表格的轴心点 JOIN ed at。



为了更好地解释如何在SQL中加入表格，请阅读以下文章，

SQL联接的可见表示 [ ^ ]

SQL Server中的连接类型 [ ^ ]

数据库规范化 - 维基百科 [ ^

For example I have table accounts with id, and table sessions with account_id. The fields are connected. So what is the usability of it?

What I have tried:

To google and to find it here.

解决方案

Those columns are used to link together the tables and their entities. Giving you a specific scenario, just think of the following content,

Account
id | name | ...
1  | ABCD | ...
2  | EFGH | ...

Sessions
id | account_id | ...
1  | 1          | ...
2  | 43         | ...
3  | 3          | ...
4  | 1          | ...
5  | 2          | ...

For example, in the states where you want to show all the sessions linked to a specific account from both the tables, you would use the ID from Account and Account_Id from Sessions table to "JOIN" them together. In SQL JOIN, you specify which records to JOIN based on which criteria — the columns.

Thus, getting something like this,

Account.id | Sessions.id | name | ...
1          | 1           | ABCD | ...
1          | 4           | ABCD | ...

Then further stuff is your own logic to use the data, how? That is all upto you, basically this is done on the tables that have been normalized. You remove a few common anomalies from the tables, and you remove some data redundancies. That step results in more than 1, 2 or even 3 tables sometimes. Thus getting the data back requires you to JOIN the tables. These columns — account.id, sessions.account_id — act as the pivot points for your tables to be JOINed at.

For a better explanation of how to JOIN the tables in SQL, please read the following articles,
Visual Representation of SQL Joins[^]
Types of Join in SQL Server[^]
Database normalization - Wikipedia[^]

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