如何将一行MySQL数据库表链接到另一个表中的另一行

问题描述：

I know it makes little sense... and i'm new to using MySQL... What i'm trying to do here is, link one tables row to another tables row... for an example there are two tables.. one table is for user registration and same table is used for login as well... and the next table is for user posts.. like status updates and all...

here is how i want it...

user_log_info:-
id ( primary )
firstname
lastname
username
email
password

posts:-
id ( primary )
userposts
posted_by
date_post

so as you can see, i want the user_log_info tables username to be automatically copied to posts posted_by row... And i have no idea how i can archive this...

我知道这没什么意义......而且我是使用MySQL的新手...... 我是谁？我试图在这里做，是将一个表行链接到另一个表行... 为一个例子，有两个表.. \无表用于用户注册，同样的表也用于登录... 和下一张表适用于用户帖子..比如状态更新和所有... p>

这里是我想要的... p>

   user_log_info： -  
id（primary）
firstname 
lastname 
username 
email 
password 
 
posts： -  
id（primary）
userposts 
posted_by 
date_post 
  code>  pre> 
 
 所以你可以看到，我希望 user_log_info  code>表的用户名自动复制到 posts  code>  posted_by  code> row ...而且我没有 我怎么能归档这个......  p> 
  div>

答

You haven't given nearly enough information to give a full answer, but I'll do my best with what you've given.

Tables

+-----------------+ +-----------------+
| users_log_info  | | posts           |
+-----------------+ +-----------------+
| int ID (primary)| | int ID (primary)|
+-----------------+ | int posted_by   |
                    +-----------------+

(I left off fields that are irrelevant to what you seem to want to do, I'm just simplifying it)

posted_by is an unofficial foreign key, or referencing the primary key of another table.

To insert, what you can do is along the lines of this:

INSERT INTO posts(...., posted_by) VALUES (...., user.ID)

Where .... is referencing all of your other information to insert

Then, to find information on someone who posted something:

SELECT * FROM users_log_info WHERE ID = Post.posted_by

Or if you want to find all posts by a user:

SELECT * FROM posts WHERE posted_by = user.ID

So, if Bob, who is User ID 3 wants to post "Hi", you might be able to do:

INSERT INTO posts(content, posted_by) VALUES('Hi', bob.ID)

And then when you are outputting the post you might do this:

post = (however you choose the post to put on the page)
userPosted = SELECT * FROM users_log_info WHERE ID = post.posted_by

print post.content + " posted by: " userPosted.Name

Essentially, the field "posted_by" is, to "posts" an arbitrary number, but you know that it links to, or references, a user. It does that by referencing "ID", which is the primary key of users_log_info, so that when you want to get information from users_log_info, is all you need to do is select the entry which has the ID that corresponds to "posted_by". I do recommend naming it something like posterID, however, for easier identification.

如何将一行MySQL数据库表链接到另一个表中的另一行

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