Keep the order of current and future posts - database

Question

One of my curiosities these days is how to order some posts. I will give you a clear example, maybe one the majority of you experimented in the past.
The Facebook Timeline, which you can add posts and events to, at any point in time you want. In this case, I assume, the posts are ordered by the date. When you add a new status for the past, you have to assign it a date, so it is easy to get them in order.
What I want to do is to have posts and the option to add a new post after a specific one. I don't have the option to add a date to it but I have to have a way to get them in that order.
So, if every post has an id and a date (the creation date). If a new post is added between 2 posts, I can't increment all the ids of the "upper" posts, so that I can order by the id. Neither is the date, because I can add a post between two older posts in the future.
What solution do you imagine for this? What criteria should I order by (I am ready to make some database scheme changes if needed)?

Answer 1

OK, there's another possible solution. Use two columns for ordering: Order1 is basic order, and Order2 is order within group defined by Order1. You assign your posts to some arbitrary groups (i.e. all posts from single day or every 100 posts) by setting Order1. Within each group posts are ordered according to value in Order2.
If a new post must be inserted into some group you only need to renumber Order2 values for posts in this particular group - not all posts in table.
Of course when retrieving the rows you order by Order1, Order2.
So your table looks like this:
PostName Order1 Order2
------------------------
A 1 1
B 1 2
C 1 3
D 1 4
E 2 1
F 2 2
G 2 3
Now if you want to insert X between F and G you renumber only items in group Order1 = 2, so that rows become:
PostName Order1 Order2
------------------------
A 1 1
B 1 2
C 1 3
D 1 4
E 2 1
F 2 2
G 2 4
X 2 3
Now, if you want to insert Z between A and B you only renumber Order2 in posts in group Order1 = 1:
PostName Order1 Order2
------------------------
A 1 1
B 1 3
C 1 4
D 1 5
E 2 1
F 2 2
G 2 4
X 2 3
Z 1 2

Answer 2

IF you're not going order by a criteria (Date, for example), you will need something to order them. Not necessary have to use column Id to order, you could add a column that is not the PK, and makes the function of ordinalPosition.
So, when you insert at the end, you will get the max ordinalPosition, and then do ordinalPosition+1.
If you want to insert between two of those, then you look the ordinal position of the two post you have (to insert between them), update incrementing in 1 all ordinalColumns, from the major of those two post, and then (now you got a "hole" in the ordinalPosition), insert the new ordinalPosition, and that will be the the minor of those two post + 1 (which equally the mayor of those two post)
Then, you will get the posts ordered by your ordinalPosition:
Select fields from Posts
-- where your criteria goes here
order by ordinalPosition
Maybe you consider that's not a good way, because everytime you insert a post between two another one, you will have to do an update - but the Db is not magic, has to order by some criteria. And have to make sure there is no posts with same order id, so probably will have to add some Unique Constraint or something as you want.
You're not gonna update very old posts probably, so I don't think will be so much update's everytime you add a posts between other two.