Add note about truncating a database from the inside

notes/psql/truncate-database.md

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+---
+title: Truncate a database from the inside
+tags:
+  - PostgreSQL
+emoji: 🐘
+---
+
+How to delete database from the inside, with only access to that database.
+
+The primary way this works is by using `pg_dump`'s ability to drop a schema before recreating it.
+
+This creates a dump of the database without any data, and with a fresh schema (drop then rebuild). This output is then `grep`'d to only contain the drops.
+
+```sh
+pg_dump -cs "postgres://<database url>" | grep DROP > drops.psql.sql
+```
+
+Now run the drops. These drops are specifically designed for this schema so should be complete and in the correct order.
+
+```sh
+psql "postgres://<database url>" < drops.psql.sql
+```