Fix incremental analyze for non-matching attnums

To merge stats in incremental analyze for root partition, we use leaf
tables' statistics. In commit b28d0297,
we fixed an issue where child attnum do not match with a root table's
attnum for the same column. After we fixed that issue with a test, that
test also exposed the bug in analyze code.

This commit fixes the issue in analyze using the similar fix in
b28d0297.

src/backend/commands/analyze.c

@@ -3752,7 +3752,10 @@ merge_leaf_stats(VacAttrStatsP stats,
 		nullCount = nullCount +
 					get_attnullfrac(relid, stats->attr->attnum) * relTuples[i];
 
-		heaptupleStats[i] = get_att_stats(relid, stats->attr->attnum);
+		const char *attname = get_relid_attribute_name(stats->attr->attrelid, stats->attr->attnum);
+		AttrNumber child_attno = get_attnum(relid, attname);
+
+		heaptupleStats[i] = get_att_stats(relid, child_attno);
 
 		// if there is no colstats, we can skip this partition's stats
 		if (!HeapTupleIsValid(heaptupleStats[i]))

src/test/regress/expected/subselect_gp.out

@@ -1734,21 +1734,23 @@ ANALYZE dedup_test1;
 ANALYZE dedup_test2;
 ANALYZE dedup_test3;
 EXPLAIN SELECT * FROM dedup_test1 INNER JOIN dedup_test2 ON dedup_test1.a= dedup_test2.e WHERE (a) IN (SELECT a FROM dedup_test3);
-                                              QUERY PLAN                                               
--------------------------------------------------------------------------------------------------------
- Gather Motion 3:1  (slice1; segments: 3)  (cost=3.31..5.46 rows=4 width=16)
-   ->  Hash Semi Join  (cost=3.31..5.46 rows=2 width=16)
-         Hash Cond: dedup_test1.a = subselect_gp.dedup_test3.a
-         ->  Hash Join  (cost=2.09..4.18 rows=2 width=16)
-               Hash Cond: dedup_test1.a = dedup_test2.e
+                                                    QUERY PLAN                                                     
+-------------------------------------------------------------------------------------------------------------------
+ Gather Motion 3:1  (slice1; segments: 3)  (cost=3.24..5.37 rows=4 width=16)
+   ->  Hash Join  (cost=3.24..5.37 rows=2 width=16)
+         Hash Cond: dedup_test1.a = dedup_test2.e
+         ->  Hash Join  (cost=1.15..3.24 rows=2 width=12)
+               Hash Cond: dedup_test1.a = subselect_gp.dedup_test3.a
                ->  Seq Scan on dedup_test1  (cost=0.00..2.04 rows=2 width=8)
-               ->  Hash  (cost=2.04..2.04 rows=2 width=8)
-                     ->  Seq Scan on dedup_test2  (cost=0.00..2.04 rows=2 width=8)
-         ->  Hash  (cost=1.10..1.10 rows=4 width=4)
-               ->  Append  (cost=0.00..1.10 rows=4 width=4)
-                     ->  Seq Scan on dedup_test3_1_prt_1 dedup_test3  (cost=0.00..1.10 rows=4 width=4)
+               ->  Hash  (cost=1.14..1.14 rows=1 width=4)
+                     ->  HashAggregate  (cost=1.12..1.14 rows=1 width=4)
+                           Group Key: subselect_gp.dedup_test3.a
+                           ->  Append  (cost=0.00..1.10 rows=4 width=4)
+                                 ->  Seq Scan on dedup_test3_1_prt_1 dedup_test3  (cost=0.00..1.10 rows=4 width=4)
+         ->  Hash  (cost=2.04..2.04 rows=2 width=8)
+               ->  Seq Scan on dedup_test2  (cost=0.00..2.04 rows=2 width=8)
  Optimizer: legacy query optimizer
-(12 rows)
+(14 rows)
 
 SELECT * FROM dedup_test1 INNER JOIN dedup_test2 ON dedup_test1.a= dedup_test2.e WHERE (a) IN (SELECT a FROM dedup_test3);
  a | b | e | f