Make EXPLAIN MERGE output format more compact

We can use a single line to print all tuple counts that MERGE processed,
for conciseness, and elide those that are zeroes.  Non-text formats
report all numbers, as is typical.

Per comment from Justin Pryzby <pryzby@telsasoft.com>

Discussion: https://postgr.es/m/20220511163350.GL19626@telsasoft.com

src/backend/commands/explain.c

@@ -4068,10 +4068,27 @@ show_modifytable_info(ModifyTableState *mtstate, List *ancestors,
 			skipped_path = total - insert_path - update_path - delete_path;
 			Assert(skipped_path >= 0);
 
-			ExplainPropertyFloat("Tuples Inserted", NULL, insert_path, 0, es);
-			ExplainPropertyFloat("Tuples Updated", NULL, update_path, 0, es);
-			ExplainPropertyFloat("Tuples Deleted", NULL, delete_path, 0, es);
-			ExplainPropertyFloat("Tuples Skipped", NULL, skipped_path, 0, es);
+			if (es->format == EXPLAIN_FORMAT_TEXT && total > 0)
+			{
+				ExplainIndentText(es);
+				appendStringInfoString(es->str, "Tuples:");
+				if (insert_path > 0)
+					appendStringInfo(es->str, " inserted=%.0f", insert_path);
+				if (update_path > 0)
+					appendStringInfo(es->str, " updated=%.0f", update_path);
+				if (delete_path > 0)
+					appendStringInfo(es->str, " deleted=%.0f", delete_path);
+				if (skipped_path > 0)
+					appendStringInfo(es->str, " skipped=%.0f", skipped_path);
+				appendStringInfoChar(es->str, '\n');
+			}
+			else
+			{
+				ExplainPropertyFloat("Tuples Inserted", NULL, insert_path, 0, es);
+				ExplainPropertyFloat("Tuples Updated", NULL, update_path, 0, es);
+				ExplainPropertyFloat("Tuples Deleted", NULL, delete_path, 0, es);
+				ExplainPropertyFloat("Tuples Skipped", NULL, skipped_path, 0, es);
+			}
 		}
 	}
 

src/test/regress/expected/merge.out

@@ -1329,10 +1329,7 @@ WHEN MATCHED THEN
                             explain_merge                             
 ----------------------------------------------------------------------
  Merge on ex_mtarget t (actual rows=0 loops=1)
-   Tuples Inserted: 0
-   Tuples Updated: 50
-   Tuples Deleted: 0
-   Tuples Skipped: 0
+   Tuples: updated=50
    ->  Merge Join (actual rows=50 loops=1)
          Merge Cond: (t.a = s.a)
          ->  Sort (actual rows=50 loops=1)
@@ -1343,7 +1340,7 @@ WHEN MATCHED THEN
                Sort Key: s.a
                Sort Method: quicksort  Memory: xxx
                ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
-(15 rows)
+(12 rows)
 
 -- only updates to selected tuples
 SELECT explain_merge('
@@ -1353,10 +1350,7 @@ WHEN MATCHED AND t.a < 10 THEN
                             explain_merge                             
 ----------------------------------------------------------------------
  Merge on ex_mtarget t (actual rows=0 loops=1)
-   Tuples Inserted: 0
-   Tuples Updated: 5
-   Tuples Deleted: 0
-   Tuples Skipped: 45
+   Tuples: updated=5 skipped=45
    ->  Merge Join (actual rows=50 loops=1)
          Merge Cond: (t.a = s.a)
          ->  Sort (actual rows=50 loops=1)
@@ -1367,7 +1361,7 @@ WHEN MATCHED AND t.a < 10 THEN
                Sort Key: s.a
                Sort Method: quicksort  Memory: xxx
                ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
-(15 rows)
+(12 rows)
 
 -- updates + deletes
 SELECT explain_merge('
@@ -1379,10 +1373,7 @@ WHEN MATCHED AND t.a >= 10 AND t.a <= 20 THEN
                             explain_merge                             
 ----------------------------------------------------------------------
  Merge on ex_mtarget t (actual rows=0 loops=1)
-   Tuples Inserted: 0
-   Tuples Updated: 5
-   Tuples Deleted: 5
-   Tuples Skipped: 40
+   Tuples: updated=5 deleted=5 skipped=40
    ->  Merge Join (actual rows=50 loops=1)
          Merge Cond: (t.a = s.a)
          ->  Sort (actual rows=50 loops=1)
@@ -1393,7 +1384,7 @@ WHEN MATCHED AND t.a >= 10 AND t.a <= 20 THEN
                Sort Key: s.a
                Sort Method: quicksort  Memory: xxx
                ->  Seq Scan on ex_msource s (actual rows=100 loops=1)
-(15 rows)
+(12 rows)
 
 -- only inserts
 SELECT explain_merge('
@@ -1403,10 +1394,7 @@ WHEN NOT MATCHED AND s.a < 10 THEN
                             explain_merge                             
 ----------------------------------------------------------------------
  Merge on ex_mtarget t (actual rows=0 loops=1)
-   Tuples Inserted: 4
-   Tuples Updated: 0
-   Tuples Deleted: 0
-   Tuples Skipped: 96
+   Tuples: inserted=4 skipped=96
    ->  Merge Left Join (actual rows=100 loops=1)
          Merge Cond: (s.a = t.a)
          ->  Sort (actual rows=100 loops=1)
@@ -1417,7 +1405,7 @@ WHEN NOT MATCHED AND s.a < 10 THEN
                Sort Key: t.a
                Sort Method: quicksort  Memory: xxx
                ->  Seq Scan on ex_mtarget t (actual rows=45 loops=1)
-(15 rows)
+(12 rows)
 
 -- all three
 SELECT explain_merge('
@@ -1431,10 +1419,7 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                             explain_merge                             
 ----------------------------------------------------------------------
  Merge on ex_mtarget t (actual rows=0 loops=1)
-   Tuples Inserted: 10
-   Tuples Updated: 9
-   Tuples Deleted: 5
-   Tuples Skipped: 76
+   Tuples: inserted=10 updated=9 deleted=5 skipped=76
    ->  Merge Left Join (actual rows=100 loops=1)
          Merge Cond: (s.a = t.a)
          ->  Sort (actual rows=100 loops=1)
@@ -1445,7 +1430,7 @@ WHEN NOT MATCHED AND s.a < 20 THEN
                Sort Key: t.a
                Sort Method: quicksort  Memory: xxx
                ->  Seq Scan on ex_mtarget t (actual rows=49 loops=1)
-(15 rows)
+(12 rows)
 
 DROP TABLE ex_msource, ex_mtarget;
 DROP FUNCTION explain_merge(text);