Populate the room version from state events

See `rooms_version_column_3.sql.postgres` for details about why we need to do
that.

synapse/storage/data_stores/main/schema/delta/57/rooms_version_column_3.sql.postgres

@@ -0,0 +1,38 @@
+/* Copyright 2020 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+-- When we first added the room_version column to the rooms table, it was populated from
+-- the current_state_events table. However, there was an issue causing a background
+-- update to clean up the current_state_events table for rooms where the server is no
+-- longer participating, before that column could be populated. Therefore, some rooms had
+-- a NULL room_version.
+
+-- The rooms_version_column_2.sql.* delta files were introduced to make the populating
+-- synchronous instead of running it in a background update, which fixed this issue.
+-- However, all of the instances of Synapse installed or updated in the meantime got
+-- their rooms table corrupted with NULL room_versions.
+
+-- This query fishes out the room versions from the create event using the state_events
+-- table instead of the current_state_events one, as the former still have all of the
+-- create events.
+
+UPDATE rooms SET room_version=(
+    SELECT COALESCE(json::json->'content'->>'room_version','1')
+    FROM state_events se INNER JOIN event_json ej USING (event_id)
+    WHERE se.room_id=rooms.room_id AND se.type='m.room.create' AND se.state_key=''
+) WHERE rooms.room_version IS NULL;
+
+-- see also rooms_version_column_3.sql.sqlite which has a copy of the above query, using
+-- sqlite syntax for the json extraction.

synapse/storage/data_stores/main/schema/delta/57/rooms_version_column_3.sql.sqlite

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+/* Copyright 2020 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+-- see rooms_version_column_3.sql.postgres for details of what's going on here.
+
+UPDATE rooms SET room_version=(
+    SELECT COALESCE(json_extract(ej.json, '$.content.room_version'), '1')
+    FROM state_events se INNER JOIN event_json ej USING (event_id)
+    WHERE se.room_id=rooms.room_id AND se.type='m.room.create' AND se.state_key=''
+) WHERE rooms.room_version IS NULL;