如何在MySQL中使用正确的外部联接将三个单独的列联接在一起？

Question

Write a SQL RIGHT OUTER JOIN statement that joins the user_id column from the blog.posts table, the name column of the blog.users table and the body column of the blog.posts table together.

Here is what I have so far:

USE blog;
SELECT posts.user_id, posts.body, users.name
  FROM posts
    RIGHT OUTER JOIN users ON
    posts.user_id, posts.body = users.name;

Here are the tables with their columns

posts: id,body,user_id
users: id, name

How do I adjust this code to work?

Answer 1

Here is the syntax for RIGHT JOIN.

SELECT column_name(s)
FROM table1
RIGHT JOIN table2 ON table1.column_name = table2.column_name;

For more details, go to this link.

https://www.w3schools.com/sql/sql_join_right.asp

Hope this helps.

Answer 2

to stick with a right join then:

SELECT posts.user_id, posts.body, users.name
  FROM posts
    RIGHT OUTER JOIN users ON posts.user_id = users.id;

but, more conventionally that is the same at this:

SELECT posts.user_id, posts.body, users.name
  FROM users
    LEFT OUTER JOIN posts ON users.id = posts.user_id;

However, I am going to hope you cannot have a blog without a user, so my guess is it really should be an inner join:

SELECT posts.user_id, posts.body, users.name
  FROM posts
    INNER JOIN users ON posts.user_id = users.id;

Answer 3

You can try like the following:

SELECT posts.user_id, posts.body, COALESCE(users.name, 'Unknown') AS user_name
  FROM Posts
       LEFT JOIN Users
          ON Posts.user_id = Users.id

Answer 4

This worked for me

USE blog;
SELECT posts.user_id, posts.body, users.name
FROM posts
RIGHT OUTER JOIN users ON
posts.user_id = users.id;

Hope this helps