Add pg Prefix Is Reserved For System Schemas as a postgres til

README.md

@@ -156,6 +156,7 @@ _310 TILs and counting..._
 - [List All Versions Of A Function](postgres/list-all-versions-of-a-function.md)
 - [List Database Users](postgres/list-database-users.md)
 - [Max Identifier Length Is 63 Bytes](postgres/max-identifier-length-is-63-bytes.md)
+- [pg Prefix Is Reserved For System Schemas](postgres/pg-prefix-is-reserved-for-system-schemas.md)
 - [Restart A Sequence](postgres/restart-a-sequence.md)
 - [Restarting Sequences When Truncating Tables](postgres/restarting-sequences-when-truncating-tables.md)
 - [Send A Command To psql](postgres/send-a-command-to-psql.md)

postgres/pg-prefix-is-reserved-for-system-schemas.md

@@ -0,0 +1,13 @@
+# pg Prefix Is Reserved For System Schemas
+
+Have you ever tried to create a schema with `pg_` as the first part of the
+name of the schema? If so, you probably didn't get very far. Postgres won't
+let you do that. It reserves the `pg_` prefix for system schemas. If you try
+to create a schema in this way, you'll get an *unacceptable schema name*
+error.
+
+```
+> create schema pg_cannot_do_this;
+ERROR:  unacceptable schema name "pg_cannot_do_this"
+DETAIL:  The prefix "pg_" is reserved for system schemas.
+```