Add Survey Of User-Defined Ordering Of Records as a Postgres TIL

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
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-_1395 TILs and counting..._
+_1396 TILs and counting..._
 
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@@ -772,6 +772,7 @@ _1395 TILs and counting..._
 - [Special Math Operators](postgres/special-math-operators.md)
 - [Storing Emails With citext](postgres/storing-emails-with-citext.md)
 - [String Contains Another String](postgres/string-contains-another-string.md)
+- [Survey Of User-Defined Ordering Of Records](postgres/survey-of-user-defined-ordering-of-records.md)
 - [Switch Non-Castable Column Type With Using Clause](postgres/switch-non-castable-column-type-with-using-clause.md)
 - [Switch The Running Postgres Server Version](postgres/switch-the-running-postgres-server-version.md)
 - [Temporarily Disable Triggers](postgres/temporarily-disable-triggers.md)

postgres/survey-of-user-defined-ordering-of-records.md

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+# Survey Of User-Defined Ordering Of Records
+
+### Approaches
+
+#### Positional Indexes
+
+Assign an integer position to everything in the list. To insert something in
+the middle of the list, you assign it that position and then increment the
+position each item in the list after it by one. Can require a lot more writes
+than other approaches.
+
+#### Positional Averaging
+
+You can insert an item between two others with a single operation by taking the
+average of the positional values (indexes) of the two surrounding items and
+making that the position of the item being inserted.
+
+- Decimal / Floating-Point - runs out of precision fairly quickly
+- Fractional / True Fractions - much more precision, trickier to implement
+- Large Int Boundaries - add first item at `0`, add second item at average of
+  `0` and `MAX_INT`. Need to insert at the front of the list, average lowest
+  index item with `MIN_INT`. [source](https://github.com/brendon/ranked-model/blob/master/lib/ranked-model.rb#L8-L11)
+
+#### LexoRank
+
+Similar to the (numeric) positional averaging approaches, but uses strings
+instead to get much more precision. Lexicographical ordering is used. To insert
+between two items, add a character to the end of the string that will position
+it between the two items.
+
+#### Stored Array
+
+Store an ordered array of element IDs either as a `jsonb` column or stringified
+JSON in a `text` column on the _collection_ table. If you have `list_items`
+that are ordered, then the `lists` table will have an `ordering` column of
+`list_items` IDs. You lose referential integrity with this approach.
+
+Here is an [example
+implementation](https://gist.github.com/jbranchaud/a00e0d6d17d562bec3007e3a4bcace94).
+
+#### Linked List
+
+A singly or doubly linked list where each item points to the next item in the list (and in the case of the doubly, points back to its previous item).
+
+[source](https://news.ycombinator.com/item?id=25802129)
+
+### References
+
+- [User-defined Order in SQL](https://begriffs.com/posts/2018-03-20-user-defined-order.html)
+- [Building Sortable Relations with PostgreSQL](https://brunoscheufler.com/blog/2022-09-26-building-sortable-relations-with-postgresql)
+- [User Defined Ordering Made Easy](https://steve.dignam.xyz/2020/03/31/practical-ordering/)
+- [Realtime Editing of Ordered Sequences](https://www.figma.com/blog/realtime-editing-of-ordered-sequences/#fractional-indexing/) (fractional indexing)
+- [Numeric and String Indexing](https://stackoverflow.com/questions/9536262/best-representation-of-an-ordered-list-in-a-database/49956113#49956113)
+- [Keeping an ordered collection in PostgreSQL](https://medium.com/the-missing-bit/keeping-an-ordered-collection-in-postgresql-9da0348c4bbe)
+- [Jira’s ranking system explained](https://tmcalm.nl/blog/lexorank-jira-ranking-system-explained/)
+- [JIRA LexoRank Explained](https://www.youtube.com/watch?v=OjQv9xMoFbg)
+- [User-defined Order in SQL | Hacker News](https://news.ycombinator.com/item?id=16635440)
+
+### Examples / Implementations
+
+- [Ranked Model - big integer positional averaging](https://github.com/brendon/ranked-model/blob/master/lib/ranked-model/ranker.rb#L174-L181)
+- [LexoRank Ruby Gem](https://github.com/richardboehme/lexorank)