Subquery pushdown investigation

part_1.sql

CREATE TABLE table_1 (key int, value int);
CREATE TABLE table_2 (key int, value int);
CREATE TABLE table_3 (key int, value int);

SET citus.shard_count TO 4;
SET citus.shard_replication_factor TO 1;

SELECT create_distributed_table ('table_1', 'key');
SELECT create_distributed_table ('table_2', 'key');
SELECT create_distributed_table ('table_3', 'key');

-- this should have errored out since it is not logically correct to push down
-- however our current logic allows the following to run and return wrong results
INSERT INTO table_1 (key)
	SELECT table_2.key FROM table_2 INNER JOIN table_3 ON (table_2.key = table_3.value);

-- same for LEFT JOIN
INSERT INTO table_1 (key)
	SELECT table_2.key FROM table_2 LEFT JOIN table_3 ON (table_2.key = table_3.value);