Add Change The Owner Of A Sequence as a Postgres TIL

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1329 TILs and counting..._
+_1330 TILs and counting..._
 
 ---
 
@@ -613,6 +613,7 @@ _1329 TILs and counting..._
 - [Between Symmetric](postgres/between-symmetric.md)
 - [Capitalize All The Words](postgres/capitalize-all-the-words.md)
 - [Change The Current Directory For psql](postgres/change-the-current-directory-for-psql.md)
+- [Change The Owner Of A Sequence](postgres/change-the-owner-of-a-sequence.md)
 - [Check If The Local Server Is Running](postgres/check-if-the-local-server-is-running.md)
 - [Check If User Role Exists For Database](postgres/check-if-user-role-exists-for-database.md)
 - [Check Table For Any Oprhaned Records](postgres/check-table-for-any-orphaned-records.md)

postgres/change-the-owner-of-a-sequence.md

@@ -0,0 +1,32 @@
+# Change The Owner Of A Sequence
+
+Sequence ownership is one of those things in PostgreSQL that is just under the
+surface and so it is easy to not know about it. If, however, you are doing a
+live migration where you are swapping out a column or entire table, you'll need
+to know about it.
+
+For instance, consider migrating a primary key column from `int` to `bigint`.
+Let's say you construct and backfill the new `bigint` column and then swap it
+out with the `int` column.
+
+Run a sequence ownership query like [the ones discussed in this
+article](https://sadique.io/blog/2019/05/07/viewing-sequence-ownership-information-in-postgres/)
+and you'll see that the original `int` column still owns the sequence.
+
+If you try to drop `old_id`, you'll fortunately get a warning from Postgres:
+
+```sql
+alter table cats drop column old_id;
+ERROR:  cannot drop column old_id of table cats because other objects depend on it
+DETAIL:  default value for column id of table cats depends on sequence cats_id_seq
+HINT:  Use DROP ... CASCADE to drop the dependent objects too.
+```
+
+The `DROP ... CASCADE` suggestion is not the thing to do here. Instead, you'll
+want to update the ownership of the sequence to the _new_ `id` column:
+
+```sql
+alter sequence cats_id_seq owned by cats.id;
+```
+
+[source](https://www.postgresql.org/docs/current/sql-altersequence.html)