Expand virtual generated columns before sublink pull-up

Currently, we expand virtual generated columns after we have pulled up
any SubLinks within the query's quals.  This ensures that the virtual
generated column references within SubLinks that should be transformed
into joins are correctly expanded.  This approach works well and has
posed no issues.

In an upcoming patch, we plan to centralize the collection of catalog
information needed early in the planner.  This will help avoid
repeated table_open/table_close calls for relations in the rangetable.
Since this information is required during sublink pull-up, we are
moving the expansion of virtual generated columns to occur beforehand.

To achieve this, if any EXISTS SubLinks can be pulled up, their
rangetables are processed just before pulling them up.

Author: Richard Guo <guofenglinux@gmail.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAMbWs4-bFJ1At4btk5wqbezdu8PLtQ3zv-aiaY3ry9Ymm=jgFQ@mail.gmail.com

1 files changed, 27 insertions, 0 deletions

diff --git a/src/backend/optimizer/plan/subselect.c b/src/backend/optimizer/plan/subselect.c
index e7cb3fede66..575303b294a 100644
--- a/src/backend/optimizer/plan/subselect.c
+++ b/src/backend/optimizer/plan/subselect.c
@@ -1454,6 +1454,7 @@ convert_EXISTS_sublink_to_join(PlannerInfo *root, SubLink *sublink,
 	Query	   *parse = root->parse;
 	Query	   *subselect = (Query *) sublink->subselect;
 	Node	   *whereClause;
+	PlannerInfo subroot;
 	int			rtoffset;
 	int			varno;
 	Relids		clause_varnos;
@@ -1516,6 +1517,32 @@ convert_EXISTS_sublink_to_join(PlannerInfo *root, SubLink *sublink,
 		return NULL;
 
 	/*
+	 * Scan the rangetable for relations with virtual generated columns, and
+	 * replace all Var nodes in the subquery that reference these columns with
+	 * the generation expressions.
+	 *
+	 * Note: we construct up an entirely dummy PlannerInfo for use here.  This
+	 * is fine because only the "glob" and "parse" links will be used in this
+	 * case.
+	 *
+	 * Note: we temporarily assign back the WHERE clause so that any virtual
+	 * generated column references within it can be expanded.  It should be
+	 * separated out again afterward.
+	 */
+	MemSet(&subroot, 0, sizeof(subroot));
+	subroot.type = T_PlannerInfo;
+	subroot.glob = root->glob;
+	subroot.parse = subselect;
+	subselect->jointree->quals = whereClause;
+	subselect = expand_virtual_generated_columns(&subroot);
+
+	/*
+	 * Now separate out the WHERE clause again.
+	 */
+	whereClause = subselect->jointree->quals;
+	subselect->jointree->quals = NULL;
+
+	/*
 	 * The subquery must have a nonempty jointree, but we can make it so.
 	 */
 	replace_empty_jointree(subselect);