change log tvf

rfcs/00xx-changelog-tvf.md

@@ -0,0 +1,82 @@
+---
+feature: changelog_tvf
+authors:
+  - "st1page"
+start_date: "2023/08/24"
+---
+
+# 
+
+Please feel free to add or remove sections.
+
+## Summary
+
+Introduce a new TVF 
+```
+changelog(table/mv name) -> Append only stream(
+  original schema | 
+  op: varchar, 
+  event_time: TIMESTAMPTZ, 
+  _row_id(hidden): Serial,
+  old_value: STRUCT<original schema>)
+```
+And users can get a append-only stream and express more flexible behavior. 
+```SQL
+  CREATE SOURCE events_source(
+    id: int, 
+    msg: varchar, 
+    status: varchar, 
+    event_time timestamptz, 
+    proc_time timestampz AS proctime()
+  );
+
+  CREATE MATERIALIZED VIEW events as
+  SELECT * FROM events_source 
+  WHERE proc_time > NOW() - INTERVAL '7 days' 
+  ORDER BY event_time;
+
+  CREATE MATERIALIZED VIEW windowed_result as 
+  SELECT 
+    window_start,
+    count(*) as all_count,
+    count(*) filter(where status = 'error') as error_count
+  FROM TUMBLE (events, event_time, INTERVAL '1 MINUTES')
+  GROUP BY window_start;
+
+  CREATE MATERIALIZED VIEW error_minutes as 
+  SELECT 
+    distinct on window_start,
+    window_start,
+  FROM changelog(windowed_result) 
+  WHERE error_count > all_count * 0.9 AND op = "insert";
+
+  CREATE MATERIALIZED VIEW detailed_msg_in_error_minutes as 
+  SELECT events.*
+  FROM error_minutes 
+  JOIN events FOR SYSTEM_TIME AS OF PROCTIME()
+  ON events.event_time between window_start AND window_start + INTERVAL '1 MINUTES';
+```
+
+
+
+## Motivation
+
+Why are you want to introduce the feature?
+
+## Design
+
+Explain the feature in detail.
+
+## Unresolved questions
+
+* Are there some questions that haven't been resolved in the RFC?
+* Can they be resolved in some future RFCs?
+* Move some meaningful comments to here.
+
+## Alternatives
+
+What other designs have been considered and what is the rationale for not choosing them?
+
+## Future possibilities
+
+Some potential extensions or optimizations can be done in the future based on the RFC.