Per @svenklemm reviews:

- Allow FROM ONLY when joining with a regular table
- Allow joining with a regular view

tsl/src/continuous_aggs/common.c

@@ -691,8 +691,10 @@ cagg_validate_query(const Query *query, const bool finalized, const char *cagg_s
 
 		if (inner_rte->rtekind == RTE_RELATION)
 		{
-			if (ts_is_hypertable(inner_rte->relid) ||
-				ts_continuous_agg_find_by_relid(inner_rte->relid))
+			bool is_hypertable = ts_is_hypertable(inner_rte->relid) ||
+								 ts_continuous_agg_find_by_relid(inner_rte->relid);
+
+			if (is_hypertable)
 			{
 				num_hypertables++;
 				if (rte == NULL)
@@ -701,18 +703,14 @@ cagg_validate_query(const Query *query, const bool finalized, const char *cagg_s
 			else
 			{
 				num_tables++;
-				if (inner_rte->relkind == RELKIND_VIEW)
-					ereport(ERROR,
-							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-							 errmsg("invalid continuous aggregate view"),
-							 errdetail("Views are not supported in continuous aggregates.")));
 			}
 
-			if (inner_rte->inh == false)
+			if (is_hypertable && inner_rte->inh == false)
 				ereport(ERROR,
 						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 						 errmsg("invalid continuous aggregate view"),
-						 errdetail("FROM ONLY is not allowed in continuous aggregate.")));
+						 errdetail(
+							 "FROM ONLY on hypertables is not allowed in continuous aggregate.")));
 		}
 
 		/* Only inner joins are allowed. */

tsl/test/expected/cagg_errors.out

@@ -204,7 +204,7 @@ Select sum(humidity), avg(temperature::int4)
 from ONLY conditions
  group by time_bucket('1week', timec) , location  WITH NO DATA;
 ERROR:  invalid continuous aggregate view
-DETAIL:  FROM ONLY is not allowed in continuous aggregate.
+DETAIL:  FROM ONLY on hypertables is not allowed in continuous aggregate.
 --grouping sets and variants
 CREATE MATERIALIZED VIEW mat_m1 WITH (timescaledb.continuous, timescaledb.materialized_only=false)
 AS

tsl/test/expected/cagg_joins.out

@@ -724,6 +724,38 @@ SELECT * FROM cagg_reorder_using;
  Wed Jun 30 17:00:00 2021 PDT | 28.0000000000000000 | thermo_3
 (16 rows)
 
+-- Cagg join with another table using FROM ONLY
+CREATE MATERIALIZED VIEW cagg_from_only
+WITH (timescaledb.continuous, timescaledb.materialized_only = FALSE) AS
+SELECT time_bucket(INTERVAL '1 day', day) AS bucket,
+   AVG(temperature),
+   name
+FROM ONLY devices JOIN conditions USING (device_id)
+GROUP BY name, bucket
+ORDER BY bucket;
+NOTICE:  refreshing continuous aggregate "cagg_from_only"
+HINT:  Use WITH NO DATA if you do not want to refresh the continuous aggregate on creation.
+SELECT * FROM cagg_from_only;
+            bucket            |         avg         |   name   
+------------------------------+---------------------+----------
+ Sun Jun 13 17:00:00 2021 PDT | 26.0000000000000000 | thermo_1
+ Mon Jun 14 17:00:00 2021 PDT | 22.0000000000000000 | thermo_2
+ Tue Jun 15 17:00:00 2021 PDT | 24.0000000000000000 | thermo_3
+ Wed Jun 16 17:00:00 2021 PDT | 24.0000000000000000 | thermo_4
+ Thu Jun 17 17:00:00 2021 PDT | 27.0000000000000000 | thermo_4
+ Fri Jun 18 17:00:00 2021 PDT | 28.0000000000000000 | thermo_4
+ Sat Jun 19 17:00:00 2021 PDT | 30.0000000000000000 | thermo_1
+ Sun Jun 20 17:00:00 2021 PDT | 31.0000000000000000 | thermo_1
+ Mon Jun 21 17:00:00 2021 PDT | 34.0000000000000000 | thermo_1
+ Tue Jun 22 17:00:00 2021 PDT | 34.0000000000000000 | thermo_2
+ Wed Jun 23 17:00:00 2021 PDT | 34.0000000000000000 | thermo_2
+ Thu Jun 24 17:00:00 2021 PDT | 32.0000000000000000 | thermo_3
+ Fri Jun 25 17:00:00 2021 PDT | 32.0000000000000000 | thermo_3
+ Sat Jun 26 17:00:00 2021 PDT | 31.0000000000000000 | thermo_3
+ Tue Jun 29 17:00:00 2021 PDT | 28.0000000000000000 | thermo_3
+ Wed Jun 30 17:00:00 2021 PDT | 28.0000000000000000 | thermo_3
+(16 rows)
+
 -- Create CAgg with join and additional WHERE conditions
 CREATE MATERIALIZED VIEW cagg_more_conds
 WITH (timescaledb.continuous, timescaledb.materialized_only = FALSE) AS
@@ -795,8 +827,8 @@ SELECT * FROM cagg_on_cagg;
 
 DROP MATERIALIZED VIEW cagg_on_cagg CASCADE;
 NOTICE:  drop cascades to 2 other objects
-DETAIL:  drop cascades to table _timescaledb_internal._hyper_17_59_chunk
-drop cascades to table _timescaledb_internal._hyper_17_60_chunk
+DETAIL:  drop cascades to table _timescaledb_internal._hyper_18_61_chunk
+drop cascades to table _timescaledb_internal._hyper_18_62_chunk
 -- Nested CAgg over a CAgg with JOIN clause
 CREATE MATERIALIZED VIEW cagg_on_cagg_join
 WITH (timescaledb.continuous, timescaledb.materialized_only=true) AS
@@ -830,8 +862,8 @@ SELECT * FROM cagg_on_cagg_join;
 
 DROP MATERIALIZED VIEW cagg_on_cagg_join CASCADE;
 NOTICE:  drop cascades to 2 other objects
-DETAIL:  drop cascades to table _timescaledb_internal._hyper_18_61_chunk
-drop cascades to table _timescaledb_internal._hyper_18_62_chunk
+DETAIL:  drop cascades to table _timescaledb_internal._hyper_19_63_chunk
+drop cascades to table _timescaledb_internal._hyper_19_64_chunk
 -- Create CAgg with join and ORDER BY
 CREATE MATERIALIZED VIEW cagg_ordered
 WITH (timescaledb.continuous, timescaledb.materialized_only = FALSE) AS
@@ -913,8 +945,8 @@ NOTICE:  refreshing continuous aggregate "cagg_nested"
 HINT:  Use WITH NO DATA if you do not want to refresh the continuous aggregate on creation.
 DROP MATERIALIZED VIEW cagg_nested CASCADE;
 NOTICE:  drop cascades to 2 other objects
-DETAIL:  drop cascades to table _timescaledb_internal._hyper_23_71_chunk
-drop cascades to table _timescaledb_internal._hyper_23_72_chunk
+DETAIL:  drop cascades to table _timescaledb_internal._hyper_24_73_chunk
+drop cascades to table _timescaledb_internal._hyper_24_74_chunk
 -- CAgg with multiple join conditions without JOIN clause
 CREATE MATERIALIZED VIEW cagg_more_joins_conds
 WITH (timescaledb.continuous, timescaledb.materialized_only = FALSE) AS
@@ -938,8 +970,7 @@ LATERAL (SELECT * FROM mat_t1 WHERE mat_t1.a = conditions.temperature) q
 GROUP BY bucket, temperature;
 NOTICE:  refreshing continuous aggregate "mat_m1"
 HINT:  Use WITH NO DATA if you do not want to refresh the continuous aggregate on creation.
--- With FROM clause has view
-\set ON_ERROR_STOP 0
+-- Joining a hypertable and view
 CREATE MATERIALIZED VIEW cagg_view
 WITH (timescaledb.continuous, timescaledb.materialized_only = TRUE) AS
 SELECT time_bucket(INTERVAL '1 day', day) AS bucket,
@@ -949,11 +980,12 @@ SELECT time_bucket(INTERVAL '1 day', day) AS bucket,
 FROM conditions, devices_view
 WHERE conditions.device_id = devices_view.device_id
 GROUP BY name, bucket, devices_view.device_id;
-ERROR:  invalid continuous aggregate view
-DETAIL:  Views are not supported in continuous aggregates.
+NOTICE:  refreshing continuous aggregate "cagg_view"
+HINT:  Use WITH NO DATA if you do not want to refresh the continuous aggregate on creation.
 CREATE TABLE cities(name text, currency text);
 INSERT INTO cities VALUES ('Berlin', 'EUR'), ('London', 'PND');
 --Error out when FROM clause has sub selects
+\set ON_ERROR_STOP 0
 CREATE MATERIALIZED VIEW conditions_summary_subselect
 WITH (timescaledb.continuous, timescaledb.materialized_only = TRUE) AS
 SELECT time_bucket(INTERVAL '1 day', day) AS bucket,
@@ -1087,6 +1119,15 @@ FROM conditions FULL JOIN devices
 ON conditions.device_id = devices.device_id
 GROUP BY name, bucket;
 ERROR:  only INNER or LEFT joins are supported in continuous aggregates
+CREATE MATERIALIZED VIEW cagg_right
+WITH (timescaledb.continuous, timescaledb.materialized_only = TRUE) AS
+SELECT time_bucket(INTERVAL '1 day', day) AS bucket,
+   AVG(temperature),
+   name
+FROM conditions RIGHT JOIN devices
+ON conditions.device_id = devices.device_id
+GROUP BY name, bucket;
+ERROR:  only INNER or LEFT joins are supported in continuous aggregates
 \set ON_ERROR_STOP 1
 CREATE MATERIALIZED VIEW cagg_left_join
 WITH (timescaledb.continuous, timescaledb.materialized_only = TRUE) AS
@@ -1098,7 +1139,7 @@ ON conditions.device_id = devices.device_id
 GROUP BY name, bucket;
 NOTICE:  refreshing continuous aggregate "cagg_left_join"
 HINT:  Use WITH NO DATA if you do not want to refresh the continuous aggregate on creation.
---Error out for join between cagg and hypertable
+-- Error out for join between cagg and hypertable
 \set ON_ERROR_STOP 0
 CREATE MATERIALIZED VIEW cagg_nested_ht
 WITH (timescaledb.continuous, timescaledb.materialized_only = TRUE) AS
@@ -1124,35 +1165,12 @@ GROUP BY bucket, devices.name, location.name;
 NOTICE:  refreshing continuous aggregate "conditions_by_day"
 HINT:  Use WITH NO DATA if you do not want to refresh the continuous aggregate on creation.
 \set VERBOSITY terse
+SET client_min_messages TO WARNING;
 DROP TABLE conditions CASCADE;
-NOTICE:  drop cascades to 67 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
-NOTICE:  drop cascades to 2 other objects
 DROP TABLE devices CASCADE;
-NOTICE:  drop cascades to view devices_view
 DROP TABLE conditions_dup CASCADE;
 DROP TABLE devices_dup CASCADE;
+RESET client_min_messages;
 \set VERBOSITY default
 -- SDC #1859
 CREATE TABLE conditions(
@@ -1193,6 +1211,7 @@ SELECT a.* FROM cagg_realtime a WHERE a.location = 'Moscow' ORDER BY bucket LIMI
 (2 rows)
 
 \set VERBOSITY terse
+SET client_min_messages TO WARNING;
 DROP TABLE conditions CASCADE;
-NOTICE:  drop cascades to 3 other objects
 DROP TABLE devices CASCADE;
+RESET client_min_messages;

tsl/test/sql/cagg_joins.sql

@@ -233,6 +233,18 @@ ORDER BY bucket;
 
 SELECT * FROM cagg_reorder_using;
 
+-- Cagg join with another table using FROM ONLY
+CREATE MATERIALIZED VIEW cagg_from_only
+WITH (timescaledb.continuous, timescaledb.materialized_only = FALSE) AS
+SELECT time_bucket(INTERVAL '1 day', day) AS bucket,
+   AVG(temperature),
+   name
+FROM ONLY devices JOIN conditions USING (device_id)
+GROUP BY name, bucket
+ORDER BY bucket;
+
+SELECT * FROM cagg_from_only;
+
 -- Create CAgg with join and additional WHERE conditions
 CREATE MATERIALIZED VIEW cagg_more_conds
 WITH (timescaledb.continuous, timescaledb.materialized_only = FALSE) AS
@@ -368,8 +380,7 @@ SELECT time_bucket(INTERVAL '1 day', day) AS bucket, temperature, count(*) from
 LATERAL (SELECT * FROM mat_t1 WHERE mat_t1.a = conditions.temperature) q
 GROUP BY bucket, temperature;
 
--- With FROM clause has view
-\set ON_ERROR_STOP 0
+-- Joining a hypertable and view
 CREATE MATERIALIZED VIEW cagg_view
 WITH (timescaledb.continuous, timescaledb.materialized_only = TRUE) AS
 SELECT time_bucket(INTERVAL '1 day', day) AS bucket,
@@ -384,6 +395,7 @@ CREATE TABLE cities(name text, currency text);
 INSERT INTO cities VALUES ('Berlin', 'EUR'), ('London', 'PND');
 
 --Error out when FROM clause has sub selects
+\set ON_ERROR_STOP 0
 CREATE MATERIALIZED VIEW conditions_summary_subselect
 WITH (timescaledb.continuous, timescaledb.materialized_only = TRUE) AS
 SELECT time_bucket(INTERVAL '1 day', day) AS bucket,
@@ -508,6 +520,15 @@ SELECT time_bucket(INTERVAL '1 day', day) AS bucket,
 FROM conditions FULL JOIN devices
 ON conditions.device_id = devices.device_id
 GROUP BY name, bucket;
+
+CREATE MATERIALIZED VIEW cagg_right
+WITH (timescaledb.continuous, timescaledb.materialized_only = TRUE) AS
+SELECT time_bucket(INTERVAL '1 day', day) AS bucket,
+   AVG(temperature),
+   name
+FROM conditions RIGHT JOIN devices
+ON conditions.device_id = devices.device_id
+GROUP BY name, bucket;
 \set ON_ERROR_STOP 1
 
 CREATE MATERIALIZED VIEW cagg_left_join
@@ -519,7 +540,7 @@ FROM conditions LEFT JOIN devices
 ON conditions.device_id = devices.device_id
 GROUP BY name, bucket;
 
---Error out for join between cagg and hypertable
+-- Error out for join between cagg and hypertable
 \set ON_ERROR_STOP 0
 CREATE MATERIALIZED VIEW cagg_nested_ht
 WITH (timescaledb.continuous, timescaledb.materialized_only = TRUE) AS
@@ -543,10 +564,12 @@ JOIN location ON location.name = devices.location
 GROUP BY bucket, devices.name, location.name;
 
 \set VERBOSITY terse
+SET client_min_messages TO WARNING;
 DROP TABLE conditions CASCADE;
 DROP TABLE devices CASCADE;
 DROP TABLE conditions_dup CASCADE;
 DROP TABLE devices_dup CASCADE;
+RESET client_min_messages;
 
 \set VERBOSITY default
 
@@ -585,5 +608,7 @@ VACUUM ANALYZE;
 SELECT a.* FROM cagg_realtime a WHERE a.location = 'Moscow' ORDER BY bucket LIMIT 2;
 
 \set VERBOSITY terse
+SET client_min_messages TO WARNING;
 DROP TABLE conditions CASCADE;
 DROP TABLE devices CASCADE;
+RESET client_min_messages;