[Caggs] Clarify ORDER BY support (github#1303)

* [Caggs] Clarify ORDER BY support

ORDER BY is supported within the ordered-set aggregates, but not in general, which has been confusing for readers. Clarify this, and also remove some repetititon which could be hard to maintain over time.

Co-authored-by: Lana Brindley <github@lanabrindley.com>
Co-authored-by: Rajakavitha Kodhandapani <krajakavitha@gmail.com>

Author: 3 people

_partials/_caggs-function-support.mdx

@@ -9,3 +9,9 @@ This table summarizes aggregate function support in continuous aggregates:
 |`DISTINCT` in aggregate functions|❌|✅|
 |`FILTER` in aggregate functions|❌|✅|
 |`ORDER BY` in aggregate functions|❌|✅|
+
+<highlight type="note">
+Note that `ORDER BY` is supported within the PostgreSQL
+[ordered-set aggregates](https://www.postgresql.org/docs/current/functions-aggregate.html).
+It is not yet supported in general.
+</highlight>

timescaledb/how-to-guides/continuous-aggregates/about-continuous-aggregates.md

@@ -66,9 +66,8 @@ and `AVG`, and non-parallelizable aggregates, such as `RANK`.
 
 In older versions of TimescaleDB, continuous aggregates only support
 [aggregate functions that can be parallelized by PostgreSQL][postgres-parallel-agg].
-They also don't support `FILTER` and `ORDER BY` clauses, and the `DISTINCT` keyword. You can
-work around this by aggregating the other parts of your query in the continuous
-aggregate, then
+You can work around this by aggregating the other parts of your query in the
+continuous aggregate, then
 [using the window function to query the aggregate][cagg-window-functions].
 
 <CaggsFunctionSupport />

timescaledb/how-to-guides/continuous-aggregates/troubleshooting.md

@@ -166,10 +166,6 @@ ERROR:  invalid continuous aggregate view
 SQL state: 0A000
 ```
 
-TimescaleDB doesn't support window functions or `JOIN` clauses on continuous
-aggregates. In versions earlier than 2.7, it doesn't support any
-[non-parallelizable SQL aggregates][postgres-parallel-agg].
-
 <CaggsFunctionSupport />
 
 ## Queries using locf() do not return NULL values

timescaledb/overview/core-concepts/continuous-aggregates.md

@@ -88,14 +88,10 @@ ORDER BY bucket;
 ```
 
 <highlight type="important">
-In TimescaleDB 2.7 and above, continuous aggregates support all PostgreSQL
-aggregate functions. They also support aggregates with keywords such as
-`DISTINCT`, `ORDER BY`, and `FILTER`. Older versions of TimescaleDB only support
-aggregate functions that can be
-[parallelized by PostgreSQL](https://www.postgresql.org/docs/current/parallel-plans.html#PARALLEL-AGGREGATION).
-They don't support `DISTINCT`, `ORDER BY`, and `FILTER`. For more information,
+Continuous aggregates support many PostgreSQL aggregate functions and features.
+Support depends on your TimescaleDB version. For a table of supported features,
 see the
-[how-to guide on continuous aggregates](/timescaledb/latest/how-to-guides/continuous-aggregates/about-continuous-aggregates/#unsupported-functions).
+[how-to guide on continuous aggregates](/timescaledb/latest/how-to-guides/continuous-aggregates/about-continuous-aggregates/#supported-functions).
 </highlight>
 
 ## Real-time aggregation