Remove redundant `room_memberships` join to find participating servers in a room (#15732)

Spawning from https://github.com/matrix-org/synapse/pull/15731

2 files changed, 3 insertions, 3 deletions

diff --git a/changelog.d/15732.doc b/changelog.d/15732.doc
new file mode 100644

index 0000000000..b0e8639df7
--- /dev/null
+++ b/changelog.d/15732.doc
@@ -0,0 +1 @@
+Simplify query to find participating servers in a room.
diff --git a/docs/usage/administration/admin_faq.md b/docs/usage/administration/admin_faq.md

index 28c3dd53a5..5c9ee7d0aa 100644
--- a/docs/usage/administration/admin_faq.md
+++ b/docs/usage/administration/admin_faq.md
@@ -27,9 +27,8 @@ What servers are currently participating in this room?
 Run this sql query on your db:
 ```sql
 SELECT DISTINCT split_part(state_key, ':', 2)
-    FROM current_state_events AS c
-    INNER JOIN room_memberships AS m USING (room_id, event_id)
-    WHERE room_id = '!cURbafjkfsMDVwdRDQ:matrix.org' AND membership = 'join';
+FROM current_state_events
+WHERE room_id = '!cURbafjkfsMDVwdRDQ:matrix.org' AND membership = 'join';
 ```
 
 What users are registered on my server?