Fix segfault creating CAgg with multiple joins

When using explicit JOIN clauses in and statement the
`Query->jointree->fromlist` will contain a list of `JoinExpr` elements
and each element have `larg` and `larg` node that can be either
`JoinExpr` or `RangeTableRef`.

Fixing it by checking the type of node before casting it properly in
order to use the `rtindex` to get the properly `RangeTblEntry`.

tsl/src/continuous_aggs/common.c

@@ -702,14 +702,30 @@ cagg_validate_query(const Query *query, const bool finalized, const char *cagg_s
 			foreach (l, query->jointree->fromlist)
 			{
 				Node *jtnode = (Node *) lfirst(l);
-				JoinExpr *join = NULL;
 				if (IsA(jtnode, JoinExpr))
 				{
-					join = castNode(JoinExpr, jtnode);
+					JoinExpr *join = castNode(JoinExpr, jtnode);
 					jointype = join->jointype;
 					op = (OpExpr *) join->quals;
-					rte = list_nth(query->rtable, ((RangeTblRef *) join->larg)->rtindex - 1);
-					rte_other = list_nth(query->rtable, ((RangeTblRef *) join->rarg)->rtindex - 1);
+
+					int lindex = 0, rindex = 0;
+
+					if (IsA(join->larg, RangeTblRef))
+						lindex = ((RangeTblRef *) join->larg)->rtindex;
+
+					if (IsA(join->larg, JoinExpr))
+						lindex = ((JoinExpr *) join->larg)->rtindex;
+
+					if (IsA(join->rarg, RangeTblRef))
+						rindex = ((RangeTblRef *) join->rarg)->rtindex;
+
+					if (IsA(join->rarg, JoinExpr))
+						rindex = ((JoinExpr *) join->rarg)->rtindex;
+
+					Assert(lindex != 0 && rindex != 0);
+
+					rte = list_nth(query->rtable, lindex - 1);
+					rte_other = list_nth(query->rtable, rindex - 1);
 					if (rte->subquery != NULL || rte_other->subquery != NULL)
 						ereport(ERROR,
 								(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),

tsl/test/expected/cagg_joins.out

@@ -49,6 +49,8 @@ DETAIL:  Migration might take a while depending on the amount of data.
 
 CREATE TABLE devices ( device_id int not null, name text, location text);
 INSERT INTO devices values (1, 'thermo_1', 'Moscow'), (2, 'thermo_2', 'Berlin'),(3, 'thermo_3', 'London'),(4, 'thermo_4', 'Stockholm');
+CREATE TABLE location (location_id INTEGER, name TEXT);
+INSERT INTO location VALUES (1, 'Moscow'), (2, 'Berlin'), (3, 'London'), (4, 'Stockholm');
 CREATE TABLE devices_dup AS SELECT * FROM devices;
 CREATE VIEW devices_view AS SELECT * FROM devices;
 -- Working cases
@@ -1115,6 +1117,18 @@ WHERE cagg.device_id = conditions.device_id
 GROUP BY 1,2,3;
 ERROR:  invalid continuous aggregate view
 DETAIL:  Views are not supported in FROM clause.
+--Multiple JOINS are not supported
+CREATE MATERIALIZED VIEW conditions_by_day WITH (timescaledb.continuous) AS
+SELECT time_bucket(INTERVAL '1 day', conditions.day) AS bucket,
+   AVG(conditions.temperature),
+   devices.name,
+   location.name
+FROM conditions
+JOIN devices ON conditions.device_id = devices.device_id
+JOIN location ON location.name = devices.location
+GROUP BY bucket, devices.name, location.name;
+ERROR:  invalid continuous aggregate view
+DETAIL:  Multiple hypertables or normal tables are not supported in FROM clause.
 \set VERBOSITY terse
 DROP TABLE conditions CASCADE;
 NOTICE:  drop cascades to 51 other objects

tsl/test/sql/cagg_joins.sql

@@ -39,6 +39,9 @@ SELECT create_hypertable(
 CREATE TABLE devices ( device_id int not null, name text, location text);
 INSERT INTO devices values (1, 'thermo_1', 'Moscow'), (2, 'thermo_2', 'Berlin'),(3, 'thermo_3', 'London'),(4, 'thermo_4', 'Stockholm');
 
+CREATE TABLE location (location_id INTEGER, name TEXT);
+INSERT INTO location VALUES (1, 'Moscow'), (2, 'Berlin'), (3, 'London'), (4, 'Stockholm');
+
 CREATE TABLE devices_dup AS SELECT * FROM devices;
 CREATE VIEW devices_view AS SELECT * FROM devices;
 
@@ -547,6 +550,17 @@ FROM cagg_cagg cagg, conditions
 WHERE cagg.device_id = conditions.device_id
 GROUP BY 1,2,3;
 
+--Multiple JOINS are not supported
+CREATE MATERIALIZED VIEW conditions_by_day WITH (timescaledb.continuous) AS
+SELECT time_bucket(INTERVAL '1 day', conditions.day) AS bucket,
+   AVG(conditions.temperature),
+   devices.name,
+   location.name
+FROM conditions
+JOIN devices ON conditions.device_id = devices.device_id
+JOIN location ON location.name = devices.location
+GROUP BY bucket, devices.name, location.name;
+
 \set VERBOSITY terse
 DROP TABLE conditions CASCADE;
 DROP TABLE devices CASCADE;