added postgres_databases_by_size.sql

sql/postgres_databases_by_size.sql

@@ -0,0 +1,21 @@
+--
+--  Author: Hari Sekhon
+--  Date: 2020-08-05 14:54:12 +0100 (Wed, 05 Aug 2020)
+--
+--  vim:ts=4:sts=4:sw=4:et
+--
+--  https://github.com/harisekhon/bash-tools
+--
+--  License: see accompanying Hari Sekhon LICENSE file
+--
+--  If you're using my code you're welcome to connect with me on LinkedIn and optionally send me feedback to help steer this or other code I publish
+--
+--  https://www.linkedin.com/in/harisekhon
+--
+
+-- List PostgreSQL databases by size descending
+
+SELECT datname,
+       pg_size_pretty(pg_database_size(datname))
+FROM pg_database
+ORDER BY pg_database_size(datname) DESC;