Database design for a simple association

After reading a lot around and receiving a hint about SQL data normalization I came with this schema. The rest will be handled by simple requests:

1. Table MRindex - All details about a entry will be listed here: key db | user_made_id | description | date | blob_picture | rss_feed | twitter_alias/keyword/hashtag |
2. Table MRtwitter - All twitter related data will be stored here: key db| index-at-table1| tw_option|tw_user | tw_date | tw_location | tw_name |tw_text
3. Table MRrss - All rss data will be stored here: key db | index-at-table1| rss_post_author | rss_post_date | rss_post_title | rss_post_text

Any comments & hints would be more than welcomed :-)

EDIT: To clarify a bit...

MRIndex (also referred as table1) holds basic data, filled by the user: Might be user tweets, hashtags or location based tweets. Once this entry is filled up

MRtwitter will hold the tweets and related info. The field index-at-table1 is the "link" to table MRindex.

MRrss it's the the same for blog posts. Same thing applies for 'index-at-table1'.

For MRindex:

description: short user description date: date of creation blob_picture: a picture if any (jpg, png, etc) rss_feed: An RSS_feed URL belonging to this user twitter_alias/keyword/hashtag: either @user, Greece (for location) or #hashtag

You can change your post_order column to a float and update the value with a calculation using the post_order values from the posts you want to end up between.

Example:

PostID, PostOrder
1       1
2       2
3       3

If you want to move PostID = 3 to be sorted between 1 and 2 it would be

PostID, PostOrder
1       1
3       1.5
2       2

Here is a SQL Fiddle with some code that moves the posts using a stored procedure where you pass in the PostID of the post to be moved and PostID of the post you want to end up behind.

SQL Fiddle

MySQL 5.5.30 Schema Setup:

create table Post
(
  PostID int primary key,
  PostOrder float unsigned not null unique,
  check (PostOrder > 0)
);

insert into Post(PostID,  PostOrder) values (1, 1);
insert into Post(PostID,  PostOrder) values (2, 2);
insert into Post(PostID,  PostOrder) values (3, 3);
insert into Post(PostID,  PostOrder) values (4, 4);
insert into Post(PostID,  PostOrder) values (5, 5);
insert into Post(PostID,  PostOrder) values (6, 6);
insert into Post(PostID,  PostOrder) values (7, 7);
insert into Post(PostID,  PostOrder) values (8, 8);
insert into Post(PostID,  PostOrder) values (9, 9);
insert into Post(PostID,  PostOrder) values (10, 10);

//

create procedure MovePost(MovePostID int, AfterPostID int)
begin

  declare AfterPostOrder float;
  declare NextPostOrder float; 


  set AfterPostOrder = (select PostOrder 
                        from Post
                        where PostID = AfterPostID);

  if AfterPostOrder is null then
    -- Move first
    set AfterPostOrder = 0;
  end if;

  set NextPostOrder = (select min(PostOrder) 
                       from Post 
                       where PostOrder > AfterPostOrder);

  if NextPostOrder is null then
    -- Move last
    set NextPostOrder = (select max(PostOrder) + 2
                         from Post);
  end if;


  update Post
  set PostOrder = (AfterPostOrder + NextPostOrder) / 2
  where PostID = MovePostID;


end

Query 1:

call MovePost (7, 3);    -- Move 7 after 3
call MovePost (8, 3);    -- Move 8 after 3
call MovePost (9, null); -- Move 9 first
call MovePost (2, 10);   -- Move 2 after 10

select * 
from Post
order by PostOrder

Results:

| POSTID | POSTORDER |
----------------------
|      9 |       0.5 |
|      1 |         1 |
|      3 |         3 |
|      8 |      3.25 |
|      7 |       3.5 |
|      4 |         4 |
|      5 |         5 |
|      6 |         6 |
|     10 |        10 |
|      2 |        11 |