[#24512] YSQL: Fix incorrect column reference to subplan with OFFSET 0

Summary:
There was a bug in our aggregate support implementation. In general, by
the execution time column references in the aggregate functions are
represented as the position number in the underlying plan's target list.
When aggregate is pushed down with the scan, the target list position
is translated to the column number of the scanned relation.

The Postgres optimizer may modify a column reference multiple times, but
in most cases a column reference is initialy represented as the column
number of some relation, as relation infos, including column lists, are
retrieved by the parser. Later on optimizer removes unused columns from
the relation infos, and updates the references accordingly, but the
initial number is stores with the reference. Hence we conveniently used
it to update the reference when we pushdown.

However, there are exceptions. Subqueries are planned independently, and
aggregates on subquery results initially refer the targets of the
subquery, not columns of some table. In most of the cases it does not
create a problem, because we do not push aggregates into subqueries. But
sometimes optimizer can figure out that subquery is trivial and flatten
it, but references' initial numbers are still point to subquery and
therefore update of pushed down column reference is incorrect.

This diff no longer relies on the assumption that the initial column
number stored with the reference is correct. It pulls the referenced
target list entry from the scan and finds there correct column number.
Jira: DB-13426

Test Plan: ./yb_build.sh --java-test 'org.yb.pgsql.TestPgRegressFeature#testPgRegressFeature'

Reviewers: jason, aagrawal, mtakahara

Reviewed By: mtakahara

Subscribers: yql

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D41415

src/postgres/src/backend/access/yb_access/yb_scan.c

@@ -2809,7 +2809,8 @@ ybcSetupTargets(YbScanDesc yb_scan, YbScanPlan scan_plan, Scan *pg_scan_plan)
  * attribute numbers from table-based numbers to index-based ones.
  */
 void
-YbDmlAppendTargetsAggregate(List *aggrefs, TupleDesc tupdesc, Relation index,
+YbDmlAppendTargetsAggregate(List *aggrefs, Scan *outer_plan,
+							TupleDesc tupdesc, Relation index,
 							bool xs_want_itup, YbcPgStatement handle)
 {
 	ListCell   *lc;
@@ -2878,18 +2879,27 @@ YbDmlAppendTargetsAggregate(List *aggrefs, TupleDesc tupdesc, Relation index,
 				}
 				else if (IsA(tle->expr, Var))
 				{
+					Var *var = castNode(Var, tle->expr);
+					int attno = var->varattno;
 					/*
-					 * Use original attribute number (varoattno) instead of projected one (varattno)
-					 * as projection is disabled for tuples produced by pushed down operators.
+					 * Change column reference in an aggregate to attribute
+					 * number. Given limited number of cases we support, we
+					 * take a number of assumptions here: the outer plan is a
+					 * plain Scan, and the scan's target list contains only
+					 * simple Vars.
+					 * Support for more generic plan shapes would require
+					 * deep rework of Postgres/PgGate interactions.
 					 */
-					int			attno = castNode(Var, tle->expr)->varattnosyn;
-
-					/*
-					 * For index only scans, translate the table-based
-					 * attribute number to an index-based one.
-					 */
-					if (index && xs_want_itup)
-						attno = YbGetIndexAttnum(index, attno);
+					if (outer_plan)
+					{
+						List *tlist = outer_plan->plan.targetlist;
+						Assert(var->varno == OUTER_VAR);
+						Assert(attno > 0);
+						Assert(attno <= list_length(tlist));
+						TargetEntry *scan_tle = list_nth_node(TargetEntry, tlist, attno - 1);
+						Assert(IsA(scan_tle->expr, Var));
+						attno = castNode(Var, scan_tle->expr)->varattno;
+					}
 					Form_pg_attribute attr = TupleDescAttr(tupdesc, attno - 1);
 					YbcPgTypeAttrs type_attrs = {attr->atttypmod};
 
@@ -3112,8 +3122,8 @@ ybcBeginScan(Relation relation,
 	 * non-aggregate and aggregate targets.
 	 */
 	if (aggrefs != NIL)
-		YbDmlAppendTargetsAggregate(aggrefs, ybScan->target_desc, index,
-									xs_want_itup, ybScan->handle);
+		YbDmlAppendTargetsAggregate(aggrefs, pg_scan_plan, ybScan->target_desc,
+									index, xs_want_itup, ybScan->handle);
 	else
 		ybcSetupTargets(ybScan, &scan_plan, pg_scan_plan);
 

src/postgres/src/backend/access/ybgin/ybginget.c

@@ -527,6 +527,7 @@ ybginDoFirstExec(IndexScanDesc scan, ScanDirection dir)
 		 * IndexOnlyScan, not IndexScan.
 		 */
 		YbDmlAppendTargetsAggregate(scan->yb_aggrefs,
+									NULL,
 									RelationGetDescr(scan->indexRelation),
 									scan->indexRelation,
 									scan->xs_want_itup,

src/postgres/src/backend/executor/yb_fdw.c

@@ -418,6 +418,7 @@ ybcSetupScanTargets(ForeignScanState *node)
 	if (node->yb_fdw_aggrefs != NIL)
 	{
 		YbDmlAppendTargetsAggregate(node->yb_fdw_aggrefs,
+									(Scan *) foreignScan,
 									RelationGetDescr(ss->ss_currentRelation),
 									NULL /* index */ ,
 									false /* xs_want_itup */ ,

src/postgres/src/include/access/yb_scan.h

@@ -280,9 +280,9 @@ extern void YbDmlAppendTargetRegular(TupleDesc tupdesc, AttrNumber attnum,
 extern void YbDmlAppendTargetRegularAttr(const FormData_pg_attribute *attr,
 										 YbcPgStatement handle);
 
-extern void YbDmlAppendTargetsAggregate(List *aggrefs, TupleDesc tupdesc,
-										Relation index, bool xs_want_itup,
-										YbcPgStatement handle);
+extern void YbDmlAppendTargetsAggregate(List *aggrefs, Scan *outer_plan,
+							TupleDesc tupdesc, Relation index,
+							bool xs_want_itup, YbcPgStatement handle);
 extern void YbDmlAppendTargets(List *colrefs, YbcPgStatement handle);
 
 extern void YbAppendPrimaryColumnRef(YbcPgStatement dml, YbcPgExpr colref);

src/postgres/src/test/regress/expected/yb_feature_select.out

@@ -321,3 +321,14 @@ SELECT	col_smallint Employee_ID,
           13 | three
           14 | four
 (9 rows)
+
+-- GHI #24512
+create table test (a bigint, b bigint);
+insert into test (a, b) select i, 2024000000000 + i from generate_series(1, 1000) as i;
+select max(sub.b) from (select b from test where (b > 2024000000000 AND b < 2025000000000) OFFSET 0 ) as sub;
+      max
+---------------
+ 2024000001000
+(1 row)
+
+drop table test;

src/postgres/src/test/regress/sql/yb_feature_select.sql

@@ -2,7 +2,7 @@
 -- YB_FEATURE Testsuite: SELECT
 --   An introduction on whether or not a feature is supported in YugaByte.
 --   This test suite does not go in depth for each command.
--- 
+--
 -- SELECT Statements
 --
 -- Select all.
@@ -117,3 +117,9 @@ SELECT	col_smallint Employee_ID,
 			 				 FROM feature_tab_dml_identifier
 							 WHERE col_id > 5)
 		ORDER BY Employee_ID;
+
+-- GHI #24512
+create table test (a bigint, b bigint);
+insert into test (a, b) select i, 2024000000000 + i from generate_series(1, 1000) as i;
+select max(sub.b) from (select b from test where (b > 2024000000000 AND b < 2025000000000) OFFSET 0 ) as sub;
+drop table test;