Fixes#6779.
DESCRIPTION: Disables citus.enable_non_colocated_router_query_pushdown
GUC by default to ensure generating a consistent distributed plan for
the queries that reference non-colocated distributed tables
We already have tests for the cases where this GUC is disabled,
so I'm not adding any more tests in this PR.
Also make multi_insert_select_window idempotent.
Related to: #6793
Some refactoring:
Consolidate expression which decides whether GROUP BY/HAVING are pushed down
Rename early pullUpIntermediateRows to hasNonDistributableAggregates
Create WorkerColumnName to handle formatting WORKER_COLUMN_FORMAT
Ignore NULL StringInfo pointers to SafeToPushdownWindowFunction
Fix bug where SubqueryPushdownMultiNodeTree mutates supplied Query,
SafeToPushdownWindowFunction requires the original query as it relies on rtable
This commit provides the support for window functions in subquery and insert
into select queries. Note that our support for window functions is still limited
because it must have a partition by clause on the distribution key. This commit
makes changes in the files insert_select_planner and multi_logical_planner. The
required tests are also added with files multi_subquery_window_functions.out
and multi_insert_select_window.out.