MySQL Forums
Forum List  »  InnoDB

Re: Denormalization to allow use UNQIUE index?
Posted by: Peter Brawley
Date: November 12, 2016 01:25PM

It's not a denormalisation issue.

You say the relation of post to comment is 1:many. Then your comment FK is misformed, referencing the comment table instead of the post table.

You need ...

CREATE TABLE post ( 
  id INT UNSIGNED NOT NULL AUTO_INCREMENT, 
  body TEXT NOT NULL, 
  issue_id INT UNSIGNED NOT NULL, 
  PRIMARY KEY (id) 
); 

CREATE TABLE comment ( 
  id int unsigned NOT NULL AUTO_INCREMENT, 
  post_id int unsigned NOT NULL, 
  body text COLLATE utf8_bin NOT NULL, 
  PRIMARY KEY (id), 
  FOREIGN KEY (post_id) REFERENCES post(id) 
);

insert into post set body='abc',issue_id=1;
insert into comment values(1,1,'def'),(2,1,'ghi');

select p.id,p.body as post,p.issue_id,c.id,c.post_id,c.body as comment 
from post p 
join comment c on p.id=c.post_id;
+----+------+----------+----+---------+---------+
| id | post | issue_id | id | post_id | comment |
+----+------+----------+----+---------+---------+
|  1 | abc  |        1 |  1 |       1 | def     |
|  1 | abc  |        1 |  2 |       1 | ghi     |
+----+------+----------+----+---------+---------+

Options: ReplyQuote


Subject
Views
Written By
Posted
Re: Denormalization to allow use UNQIUE index?
350
November 12, 2016 01:25PM


Sorry, you can't reply to this topic. It has been closed.

Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent the opinion of Oracle or any other party.