Fix pg_stat_statements for MERGE

We weren't jumbling the merge action list, so wildly different commands
would be considered to use the same query ID.  Add that, mention it in
the docs, and some test lines.

Backpatch to 15.

Author: Tatsu <bt22nakamorit@oss.nttdata.com>
Reviewed-by: Julien Rouhaud <rjuju123@gmail.com>
Discussion: https://postgr.es/m/d87e391694db75a038abc3b2597828e8@oss.nttdata.com

contrib/pg_stat_statements/expected/pg_stat_statements.out

@@ -222,12 +222,51 @@ SELECT * FROM test WHERE a IN (1, 2, 3, 4, 5);
  3 | c                   
 (8 rows)
 
+-- MERGE
+MERGE INTO test USING test st ON (st.a = test.a AND st.a >= 4)
+ WHEN MATCHED THEN UPDATE SET b = st.b || st.a::text;
+MERGE INTO test USING test st ON (st.a = test.a AND st.a >= 4)
+ WHEN MATCHED THEN UPDATE SET b = test.b || st.a::text;
+MERGE INTO test USING test st ON (st.a = test.a AND st.a >= 4)
+ WHEN MATCHED AND length(st.b) > 1 THEN UPDATE SET b = test.b || st.a::text;
+MERGE INTO test USING test st ON (st.a = test.a)
+ WHEN NOT MATCHED THEN INSERT (a, b) VALUES (0, NULL);
+MERGE INTO test USING test st ON (st.a = test.a)
+ WHEN NOT MATCHED THEN INSERT VALUES (0, NULL);	-- same as above
+MERGE INTO test USING test st ON (st.a = test.a)
+ WHEN NOT MATCHED THEN INSERT (b, a) VALUES (NULL, 0);
+MERGE INTO test USING test st ON (st.a = test.a)
+ WHEN NOT MATCHED THEN INSERT (a) VALUES (0);
+MERGE INTO test USING test st ON (st.a = test.a AND st.a >= 4)
+ WHEN MATCHED THEN DELETE;
+MERGE INTO test USING test st ON (st.a = test.a AND st.a >= 4)
+ WHEN MATCHED THEN DO NOTHING;
+MERGE INTO test USING test st ON (st.a = test.a AND st.a >= 4)
+ WHEN NOT MATCHED THEN DO NOTHING;
 SELECT query, calls, rows FROM pg_stat_statements ORDER BY query COLLATE "C";
                                     query                                     | calls | rows 
 ------------------------------------------------------------------------------+-------+------
  DELETE FROM test WHERE a > $1                                                |     1 |    1
  INSERT INTO test (a, b) VALUES ($1, $2), ($3, $4), ($5, $6)                  |     1 |    3
  INSERT INTO test VALUES(generate_series($1, $2), $3)                         |     1 |   10
+ MERGE INTO test USING test st ON (st.a = test.a AND st.a >= $1)             +|     1 |    6
+  WHEN MATCHED AND length(st.b) > $2 THEN UPDATE SET b = test.b || st.a::text |       | 
+ MERGE INTO test USING test st ON (st.a = test.a AND st.a >= $1)             +|     1 |    6
+  WHEN MATCHED THEN DELETE                                                    |       | 
+ MERGE INTO test USING test st ON (st.a = test.a AND st.a >= $1)             +|     1 |    0
+  WHEN MATCHED THEN DO NOTHING                                                |       | 
+ MERGE INTO test USING test st ON (st.a = test.a AND st.a >= $1)             +|     1 |    6
+  WHEN MATCHED THEN UPDATE SET b = st.b || st.a::text                         |       | 
+ MERGE INTO test USING test st ON (st.a = test.a AND st.a >= $1)             +|     1 |    6
+  WHEN MATCHED THEN UPDATE SET b = test.b || st.a::text                       |       | 
+ MERGE INTO test USING test st ON (st.a = test.a AND st.a >= $1)             +|     1 |    0
+  WHEN NOT MATCHED THEN DO NOTHING                                            |       | 
+ MERGE INTO test USING test st ON (st.a = test.a)                            +|     1 |    0
+  WHEN NOT MATCHED THEN INSERT (a) VALUES ($1)                                |       | 
+ MERGE INTO test USING test st ON (st.a = test.a)                            +|     2 |    0
+  WHEN NOT MATCHED THEN INSERT (a, b) VALUES ($1, $2)                         |       | 
+ MERGE INTO test USING test st ON (st.a = test.a)                            +|     1 |    0
+  WHEN NOT MATCHED THEN INSERT (b, a) VALUES ($1, $2)                         |       | 
  SELECT * FROM test ORDER BY a                                                |     1 |   12
  SELECT * FROM test WHERE a > $1 ORDER BY a                                   |     2 |    4
  SELECT * FROM test WHERE a IN ($1, $2, $3, $4, $5)                           |     1 |    8
@@ -235,7 +274,7 @@ SELECT query, calls, rows FROM pg_stat_statements ORDER BY query COLLATE "C";
  SELECT query, calls, rows FROM pg_stat_statements ORDER BY query COLLATE "C" |     0 |    0
  UPDATE test SET b = $1 WHERE a = $2                                          |     6 |    6
  UPDATE test SET b = $1 WHERE a > $2                                          |     1 |    3
-(10 rows)
+(19 rows)
 
 --
 -- INSERT, UPDATE, DELETE on test table to validate WAL generation metrics

contrib/pg_stat_statements/sql/pg_stat_statements.sql

@@ -100,6 +100,28 @@ SELECT * FROM test ORDER BY a;
 -- SELECT with IN clause
 SELECT * FROM test WHERE a IN (1, 2, 3, 4, 5);
 
+-- MERGE
+MERGE INTO test USING test st ON (st.a = test.a AND st.a >= 4)
+ WHEN MATCHED THEN UPDATE SET b = st.b || st.a::text;
+MERGE INTO test USING test st ON (st.a = test.a AND st.a >= 4)
+ WHEN MATCHED THEN UPDATE SET b = test.b || st.a::text;
+MERGE INTO test USING test st ON (st.a = test.a AND st.a >= 4)
+ WHEN MATCHED AND length(st.b) > 1 THEN UPDATE SET b = test.b || st.a::text;
+MERGE INTO test USING test st ON (st.a = test.a)
+ WHEN NOT MATCHED THEN INSERT (a, b) VALUES (0, NULL);
+MERGE INTO test USING test st ON (st.a = test.a)
+ WHEN NOT MATCHED THEN INSERT VALUES (0, NULL);	-- same as above
+MERGE INTO test USING test st ON (st.a = test.a)
+ WHEN NOT MATCHED THEN INSERT (b, a) VALUES (NULL, 0);
+MERGE INTO test USING test st ON (st.a = test.a)
+ WHEN NOT MATCHED THEN INSERT (a) VALUES (0);
+MERGE INTO test USING test st ON (st.a = test.a AND st.a >= 4)
+ WHEN MATCHED THEN DELETE;
+MERGE INTO test USING test st ON (st.a = test.a AND st.a >= 4)
+ WHEN MATCHED THEN DO NOTHING;
+MERGE INTO test USING test st ON (st.a = test.a AND st.a >= 4)
+ WHEN NOT MATCHED THEN DO NOTHING;
+
 SELECT query, calls, rows FROM pg_stat_statements ORDER BY query COLLATE "C";
 
 --

doc/src/sgml/pgstatstatements.sgml

@@ -487,7 +487,7 @@
 
   <para>
    Plannable queries (that is, <command>SELECT</command>, <command>INSERT</command>,
-   <command>UPDATE</command>, and <command>DELETE</command>) are combined into a single
+   <command>UPDATE</command>, <command>DELETE</command>, and <command>MERGE</command>) are combined into a single
    <structname>pg_stat_statements</structname> entry whenever they have identical query
    structures according to an internal hash calculation.  Typically, two
    queries will be considered the same for this purpose if they are
@@ -783,7 +783,7 @@
       <varname>pg_stat_statements.track_utility</varname> controls whether
       utility commands are tracked by the module.  Utility commands are
       all those other than <command>SELECT</command>, <command>INSERT</command>,
-      <command>UPDATE</command> and <command>DELETE</command>.
+      <command>UPDATE</command>, <command>DELETE</command>, and <command>MERGE</command>.
       The default value is <literal>on</literal>.
       Only superusers can change this setting.
      </para>

src/backend/nodes/nodeFuncs.c

@@ -2259,10 +2259,10 @@ expression_tree_walker_impl(Node *node,
 			{
 				MergeAction *action = (MergeAction *) node;
 
-				if (WALK(action->targetList))
-					return true;
 				if (WALK(action->qual))
 					return true;
+				if (WALK(action->targetList))
+					return true;
 			}
 			break;
 		case T_PartitionPruneStepOp:

src/backend/utils/misc/queryjumble.c

@@ -248,6 +248,7 @@ JumbleQueryInternal(JumbleState *jstate, Query *query)
 	JumbleExpr(jstate, (Node *) query->cteList);
 	JumbleRangeTable(jstate, query->rtable);
 	JumbleExpr(jstate, (Node *) query->jointree);
+	JumbleExpr(jstate, (Node *) query->mergeActionList);
 	JumbleExpr(jstate, (Node *) query->targetList);
 	JumbleExpr(jstate, (Node *) query->onConflict);
 	JumbleExpr(jstate, (Node *) query->returningList);
@@ -738,6 +739,16 @@ JumbleExpr(JumbleState *jstate, Node *node)
 				JumbleExpr(jstate, (Node *) conf->exclRelTlist);
 			}
 			break;
+		case T_MergeAction:
+			{
+				MergeAction *mergeaction = (MergeAction *) node;
+
+				APP_JUMB(mergeaction->matched);
+				APP_JUMB(mergeaction->commandType);
+				JumbleExpr(jstate, mergeaction->qual);
+				JumbleExpr(jstate, (Node *) mergeaction->targetList);
+			}
+			break;
 		case T_List:
 			foreach(temp, (List *) node)
 			{