Fix attnum remapping in generateClonedExtStatsStmt()

When cloning extended statistics via CREATE TABLE ... LIKE ... INCLUDING
STATISTICS, stxkeys holds attribute numbers from the source (parent)
table, but get_attname() was being called with the child relation's
OID.  If the parent has dropped columns, the child's attribute numbers
are renumbered sequentially and no longer match, so the lookup either
returns the wrong column name (silent corruption) or errors out when
the attnum does not exist in the child.

Fix it by remapping the parent attnum through attmap before the lookup,
consistent with how expression statistics are already handled a few
lines below.

Add a regression test covering both manifestations: a 3-column parent
where the stale attnum refers to no child column (cache-lookup error),
and a 4-column parent where the stale attnum silently refers to the
wrong child column.

Author: Julien Tachoires <julmon@gmail.com>
Reviewed-by: Srinath Reddy Sadipiralla <srinath2133@gmail.com>
Discussion: https://postgr.es/m/20260415105718.tomuncfbmlt67oel@poseidon.home.virt
Backpatch-through: 14

src/backend/parser/parse_utilcmd.c

@@ -2040,7 +2040,10 @@ generateClonedIndexStmt(RangeVar *heapRel, Relation source_idx,
  * extended statistic "source_statsid", for the rel identified by heapRel and
  * heapRelid.
  *
- * Attribute numbers in expression Vars are adjusted according to attmap.
+ * stxkeys in the source statistic holds attribute numbers from the parent
+ * relation.  Those attnums, along with the attribute numbers referenced by
+ * Vars inside the expression tree, are remapped to the new relation's
+ * numbering according to attmap.
  */
 static CreateStatsStmt *
 generateClonedExtStatsStmt(RangeVar *heapRel, Oid heapRelid,
@@ -2098,7 +2101,8 @@ generateClonedExtStatsStmt(RangeVar *heapRel, Oid heapRelid,
 		StatsElem  *selem = makeNode(StatsElem);
 		AttrNumber	attnum = statsrec->stxkeys.values[i];
 
-		selem->name = get_attname(heapRelid, attnum, false);
+		selem->name =
+			get_attname(heapRelid, attmap->attnums[attnum - 1], false);
 		selem->expr = NULL;
 
 		def_names = lappend(def_names, selem);

src/test/regress/expected/create_table_like.out

@@ -694,6 +694,37 @@ SELECT attname, attcompression FROM pg_attribute
  e       | 
 (5 rows)
 
+-- LIKE ... INCLUDING STATISTICS with dropped columns in the parent,
+-- so stxkeys attnums are not contiguous.
+CREATE TABLE ctl_stats3_parent (a int, b int, c int);
+ALTER TABLE ctl_stats3_parent DROP COLUMN b;
+CREATE STATISTICS ctl_stats3_stat ON a, c FROM ctl_stats3_parent;
+CREATE TABLE ctl_stats3_child (LIKE ctl_stats3_parent INCLUDING STATISTICS);
+CREATE TABLE ctl_stats4_parent (a int, b int, c int, d int);
+ALTER TABLE ctl_stats4_parent DROP COLUMN b;
+CREATE STATISTICS ctl_stats4_stat ON a, c FROM ctl_stats4_parent;
+CREATE TABLE ctl_stats4_child (LIKE ctl_stats4_parent INCLUDING STATISTICS);
+SELECT s.stxrelid::regclass AS relation,
+       array_agg(a.attname ORDER BY u.ord) AS stats_columns
+FROM pg_statistic_ext s
+CROSS JOIN LATERAL
+  unnest(s.stxkeys::int2[]) WITH ORDINALITY AS u(attnum, ord)
+JOIN pg_attribute a
+  ON a.attrelid = s.stxrelid AND a.attnum = u.attnum
+WHERE s.stxrelid IN ('ctl_stats3_child'::regclass,
+                     'ctl_stats4_child'::regclass)
+GROUP BY s.stxrelid
+ORDER BY s.stxrelid::regclass::text;
+     relation     | stats_columns 
+------------------+---------------
+ ctl_stats3_child | {a,c}
+ ctl_stats4_child | {a,c}
+(2 rows)
+
+DROP TABLE ctl_stats3_parent;
+DROP TABLE ctl_stats3_child;
+DROP TABLE ctl_stats4_parent;
+DROP TABLE ctl_stats4_child;
 DROP TABLE ctl_table;
 DROP FOREIGN TABLE ctl_foreign_table1;
 DROP FOREIGN TABLE ctl_foreign_table2;

src/test/regress/sql/create_table_like.sql

@@ -276,6 +276,32 @@ CREATE FOREIGN TABLE ctl_foreign_table2(LIKE ctl_table INCLUDING ALL) SERVER ctl
 SELECT attname, attcompression FROM pg_attribute
   WHERE attrelid = 'ctl_foreign_table2'::regclass and attnum > 0 ORDER BY attnum;
 
+-- LIKE ... INCLUDING STATISTICS with dropped columns in the parent,
+-- so stxkeys attnums are not contiguous.
+CREATE TABLE ctl_stats3_parent (a int, b int, c int);
+ALTER TABLE ctl_stats3_parent DROP COLUMN b;
+CREATE STATISTICS ctl_stats3_stat ON a, c FROM ctl_stats3_parent;
+CREATE TABLE ctl_stats3_child (LIKE ctl_stats3_parent INCLUDING STATISTICS);
+CREATE TABLE ctl_stats4_parent (a int, b int, c int, d int);
+ALTER TABLE ctl_stats4_parent DROP COLUMN b;
+CREATE STATISTICS ctl_stats4_stat ON a, c FROM ctl_stats4_parent;
+CREATE TABLE ctl_stats4_child (LIKE ctl_stats4_parent INCLUDING STATISTICS);
+SELECT s.stxrelid::regclass AS relation,
+       array_agg(a.attname ORDER BY u.ord) AS stats_columns
+FROM pg_statistic_ext s
+CROSS JOIN LATERAL
+  unnest(s.stxkeys::int2[]) WITH ORDINALITY AS u(attnum, ord)
+JOIN pg_attribute a
+  ON a.attrelid = s.stxrelid AND a.attnum = u.attnum
+WHERE s.stxrelid IN ('ctl_stats3_child'::regclass,
+                     'ctl_stats4_child'::regclass)
+GROUP BY s.stxrelid
+ORDER BY s.stxrelid::regclass::text;
+DROP TABLE ctl_stats3_parent;
+DROP TABLE ctl_stats3_child;
+DROP TABLE ctl_stats4_parent;
+DROP TABLE ctl_stats4_child;
+
 DROP TABLE ctl_table;
 DROP FOREIGN TABLE ctl_foreign_table1;
 DROP FOREIGN TABLE ctl_foreign_table2;