Add OLD/NEW support to RETURNING in DML queries.

This allows the RETURNING list of INSERT/UPDATE/DELETE/MERGE queries
to explicitly return old and new values by using the special aliases
"old" and "new", which are automatically added to the query (if not
already defined) while parsing its RETURNING list, allowing things
like:

  RETURNING old.colname, new.colname, ...

  RETURNING old.*, new.*

Additionally, a new syntax is supported, allowing the names "old" and
"new" to be changed to user-supplied alias names, e.g.:

  RETURNING WITH (OLD AS o, NEW AS n) o.colname, n.colname, ...

This is useful when the names "old" and "new" are already defined,
such as inside trigger functions, allowing backwards compatibility to
be maintained -- the interpretation of any existing queries that
happen to already refer to relations called "old" or "new", or use
those as aliases for other relations, is not changed.

For an INSERT, old values will generally be NULL, and for a DELETE,
new values will generally be NULL, but that may change for an INSERT
with an ON CONFLICT ... DO UPDATE clause, or if a query rewrite rule
changes the command type. Therefore, we put no restrictions on the use
of old and new in any DML queries.

Dean Rasheed, reviewed by Jian He and Jeff Davis.

Discussion: https://postgr.es/m/CAEZATCWx0J0-v=Qjc6gXzR=KtsdvAE7Ow=D=mu50AgOe+pvisQ@mail.gmail.com

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -4975,12 +4975,12 @@ INSERT INTO ft2 (c1,c2,c3) SELECT c1+1000,c2+100, c3 || c3 FROM ft2 LIMIT 20;
 
 INSERT INTO ft2 (c1,c2,c3) SELECT c1+1000,c2+100, c3 || c3 FROM ft2 LIMIT 20;
 INSERT INTO ft2 (c1,c2,c3)
-  VALUES (1101,201,'aaa'), (1102,202,'bbb'), (1103,203,'ccc') RETURNING *;
-  c1  | c2  | c3  | c4 | c5 | c6 |     c7     | c8 
-------+-----+-----+----+----+----+------------+----
- 1101 | 201 | aaa |    |    |    | ft2        | 
- 1102 | 202 | bbb |    |    |    | ft2        | 
- 1103 | 203 | ccc |    |    |    | ft2        | 
+  VALUES (1101,201,'aaa'), (1102,202,'bbb'), (1103,203,'ccc') RETURNING old, new, old.*, new.*;
+ old |               new               | c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8 |  c1  | c2  | c3  | c4 | c5 | c6 |     c7     | c8 
+-----+---------------------------------+----+----+----+----+----+----+----+----+------+-----+-----+----+----+----+------------+----
+     | (1101,201,aaa,,,,"ft2       ",) |    |    |    |    |    |    |    |    | 1101 | 201 | aaa |    |    |    | ft2        | 
+     | (1102,202,bbb,,,,"ft2       ",) |    |    |    |    |    |    |    |    | 1102 | 202 | bbb |    |    |    | ft2        | 
+     | (1103,203,ccc,,,,"ft2       ",) |    |    |    |    |    |    |    |    | 1103 | 203 | ccc |    |    |    | ft2        | 
 (3 rows)
 
 INSERT INTO ft2 (c1,c2,c3) VALUES (1104,204,'ddd'), (1105,205,'eee');
@@ -5111,6 +5111,31 @@ UPDATE ft2 SET c2 = c2 + 400, c3 = c3 || '_update7' WHERE c1 % 10 = 7 RETURNING
  1017 | 507 | 0001700017_update7 |                              |                          |    | ft2        | 
 (102 rows)
 
+BEGIN;
+  EXPLAIN (verbose, costs off)
+  UPDATE ft2 SET c2 = c2 + 400, c3 = c3 || '_update7b' WHERE c1 % 10 = 7 AND c1 < 40
+    RETURNING old.*, new.*;                                                         -- can't be pushed down
+                                                                  QUERY PLAN                                                                  
+----------------------------------------------------------------------------------------------------------------------------------------------
+ Update on public.ft2
+   Output: old.c1, old.c2, old.c3, old.c4, old.c5, old.c6, old.c7, old.c8, new.c1, new.c2, new.c3, new.c4, new.c5, new.c6, new.c7, new.c8
+   Remote SQL: UPDATE "S 1"."T 1" SET c2 = $2, c3 = $3 WHERE ctid = $1 RETURNING "C 1", c2, c3, c4, c5, c6, c7, c8
+   ->  Foreign Scan on public.ft2
+         Output: (c2 + 400), (c3 || '_update7b'::text), ctid, ft2.*
+         Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8, ctid FROM "S 1"."T 1" WHERE (("C 1" < 40)) AND ((("C 1" % 10) = 7)) FOR UPDATE
+(6 rows)
+
+  UPDATE ft2 SET c2 = c2 + 400, c3 = c3 || '_update7b' WHERE c1 % 10 = 7 AND c1 < 40
+    RETURNING old.*, new.*;
+ c1 | c2  |      c3       |              c4              |            c5            | c6 |     c7     | c8  | c1 | c2  |           c3           |              c4              |            c5            | c6 |     c7     | c8  
+----+-----+---------------+------------------------------+--------------------------+----+------------+-----+----+-----+------------------------+------------------------------+--------------------------+----+------------+-----
+  7 | 407 | 00007_update7 | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo |  7 | 807 | 00007_update7_update7b | Thu Jan 08 00:00:00 1970 PST | Thu Jan 08 00:00:00 1970 | 7  | 7          | foo
+ 17 | 407 | 00017_update7 | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo | 17 | 807 | 00017_update7_update7b | Sun Jan 18 00:00:00 1970 PST | Sun Jan 18 00:00:00 1970 | 7  | 7          | foo
+ 27 | 407 | 00027_update7 | Wed Jan 28 00:00:00 1970 PST | Wed Jan 28 00:00:00 1970 | 7  | 7          | foo | 27 | 807 | 00027_update7_update7b | Wed Jan 28 00:00:00 1970 PST | Wed Jan 28 00:00:00 1970 | 7  | 7          | foo
+ 37 | 407 | 00037_update7 | Sat Feb 07 00:00:00 1970 PST | Sat Feb 07 00:00:00 1970 | 7  | 7          | foo | 37 | 807 | 00037_update7_update7b | Sat Feb 07 00:00:00 1970 PST | Sat Feb 07 00:00:00 1970 | 7  | 7          | foo
+(4 rows)
+
+ROLLBACK;
 EXPLAIN (verbose, costs off)
 UPDATE ft2 SET c2 = ft2.c2 + 500, c3 = ft2.c3 || '_update9', c7 = DEFAULT
   FROM ft1 WHERE ft1.c1 = ft2.c2 AND ft1.c1 % 10 = 9;                               -- can be pushed down
@@ -5241,6 +5266,29 @@ DELETE FROM ft2 WHERE c1 % 10 = 5 RETURNING c1, c4;
  1105 | 
 (103 rows)
 
+BEGIN;
+  EXPLAIN (verbose, costs off)
+  DELETE FROM ft2 WHERE c1 % 10 = 6 AND c1 < 40 RETURNING old.c1, c4;               -- can't be pushed down
+                                                QUERY PLAN                                                 
+-----------------------------------------------------------------------------------------------------------
+ Delete on public.ft2
+   Output: old.c1, c4
+   Remote SQL: DELETE FROM "S 1"."T 1" WHERE ctid = $1 RETURNING "C 1", c4
+   ->  Foreign Scan on public.ft2
+         Output: ctid
+         Remote SQL: SELECT ctid FROM "S 1"."T 1" WHERE (("C 1" < 40)) AND ((("C 1" % 10) = 6)) FOR UPDATE
+(6 rows)
+
+  DELETE FROM ft2 WHERE c1 % 10 = 6 AND c1 < 40 RETURNING old.c1, c4;
+ c1 |              c4              
+----+------------------------------
+  6 | Wed Jan 07 00:00:00 1970 PST
+ 16 | Sat Jan 17 00:00:00 1970 PST
+ 26 | Tue Jan 27 00:00:00 1970 PST
+ 36 | Fri Feb 06 00:00:00 1970 PST
+(4 rows)
+
+ROLLBACK;
 EXPLAIN (verbose, costs off)
 DELETE FROM ft2 USING ft1 WHERE ft1.c1 = ft2.c2 AND ft1.c1 % 10 = 2;                -- can be pushed down
                                                          QUERY PLAN                                                         
@@ -6165,6 +6213,70 @@ UPDATE ft2 SET c3 = 'foo'
  (1296,96,foo,,,,"ft2       ",) | 1296 | 96 | foo |    |    |    | ft2        |    | (96,97,AAA096) | 96 | 97 | AAA096
 (16 rows)
 
+BEGIN;
+  EXPLAIN (verbose, costs off)
+  UPDATE ft2 SET c3 = 'bar'
+    FROM ft4 INNER JOIN ft5 ON (ft4.c1 = ft5.c1)
+    WHERE ft2.c1 > 1200 AND ft2.c2 = ft4.c1
+    RETURNING old, new, ft2, ft2.*, ft4, ft4.*;  -- can't be pushed down
+                                                                                                                                                                                                                                     QUERY PLAN                                                                                                                                                                                                                                     
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Update on public.ft2
+   Output: old.*, new.*, ft2.*, ft2.c1, ft2.c2, ft2.c3, ft2.c4, ft2.c5, ft2.c6, ft2.c7, ft2.c8, ft4.*, ft4.c1, ft4.c2, ft4.c3
+   Remote SQL: UPDATE "S 1"."T 1" SET c3 = $2 WHERE ctid = $1 RETURNING "C 1", c2, c3, c4, c5, c6, c7, c8
+   ->  Foreign Scan
+         Output: 'bar'::text, ft2.ctid, ft2.*, ft4.*, ft5.*, ft4.c1, ft4.c2, ft4.c3
+         Relations: ((public.ft2) INNER JOIN (public.ft4)) INNER JOIN (public.ft5)
+         Remote SQL: SELECT r1.ctid, CASE WHEN (r1.*)::text IS NOT NULL THEN ROW(r1."C 1", r1.c2, r1.c3, r1.c4, r1.c5, r1.c6, r1.c7, r1.c8) END, CASE WHEN (r2.*)::text IS NOT NULL THEN ROW(r2.c1, r2.c2, r2.c3) END, CASE WHEN (r3.*)::text IS NOT NULL THEN ROW(r3.c1, r3.c2, r3.c3) END, r2.c1, r2.c2, r2.c3 FROM (("S 1"."T 1" r1 INNER JOIN "S 1"."T 3" r2 ON (((r1.c2 = r2.c1)) AND ((r1."C 1" > 1200)))) INNER JOIN "S 1"."T 4" r3 ON (((r2.c1 = r3.c1)))) FOR UPDATE OF r1
+         ->  Nested Loop
+               Output: ft2.ctid, ft2.*, ft4.*, ft5.*, ft4.c1, ft4.c2, ft4.c3
+               Join Filter: (ft4.c1 = ft5.c1)
+               ->  Sort
+                     Output: ft2.ctid, ft2.*, ft2.c2, ft4.*, ft4.c1, ft4.c2, ft4.c3
+                     Sort Key: ft2.c2
+                     ->  Hash Join
+                           Output: ft2.ctid, ft2.*, ft2.c2, ft4.*, ft4.c1, ft4.c2, ft4.c3
+                           Hash Cond: (ft2.c2 = ft4.c1)
+                           ->  Foreign Scan on public.ft2
+                                 Output: ft2.ctid, ft2.*, ft2.c2
+                                 Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8, ctid FROM "S 1"."T 1" WHERE (("C 1" > 1200)) FOR UPDATE
+                           ->  Hash
+                                 Output: ft4.*, ft4.c1, ft4.c2, ft4.c3
+                                 ->  Foreign Scan on public.ft4
+                                       Output: ft4.*, ft4.c1, ft4.c2, ft4.c3
+                                       Remote SQL: SELECT c1, c2, c3 FROM "S 1"."T 3"
+               ->  Materialize
+                     Output: ft5.*, ft5.c1
+                     ->  Foreign Scan on public.ft5
+                           Output: ft5.*, ft5.c1
+                           Remote SQL: SELECT c1, c2, c3 FROM "S 1"."T 4"
+(29 rows)
+
+  UPDATE ft2 SET c3 = 'bar'
+    FROM ft4 INNER JOIN ft5 ON (ft4.c1 = ft5.c1)
+    WHERE ft2.c1 > 1200 AND ft2.c2 = ft4.c1
+    RETURNING old, new, ft2, ft2.*, ft4, ft4.*;
+              old               |              new               |              ft2               |  c1  | c2 | c3  | c4 | c5 | c6 |     c7     | c8 |      ft4       | c1 | c2 |   c3   
+--------------------------------+--------------------------------+--------------------------------+------+----+-----+----+----+----+------------+----+----------------+----+----+--------
+ (1206,6,foo,,,,"ft2       ",)  | (1206,6,bar,,,,"ft2       ",)  | (1206,6,bar,,,,"ft2       ",)  | 1206 |  6 | bar |    |    |    | ft2        |    | (6,7,AAA006)   |  6 |  7 | AAA006
+ (1212,12,foo,,,,"ft2       ",) | (1212,12,bar,,,,"ft2       ",) | (1212,12,bar,,,,"ft2       ",) | 1212 | 12 | bar |    |    |    | ft2        |    | (12,13,AAA012) | 12 | 13 | AAA012
+ (1224,24,foo,,,,"ft2       ",) | (1224,24,bar,,,,"ft2       ",) | (1224,24,bar,,,,"ft2       ",) | 1224 | 24 | bar |    |    |    | ft2        |    | (24,25,AAA024) | 24 | 25 | AAA024
+ (1230,30,foo,,,,"ft2       ",) | (1230,30,bar,,,,"ft2       ",) | (1230,30,bar,,,,"ft2       ",) | 1230 | 30 | bar |    |    |    | ft2        |    | (30,31,AAA030) | 30 | 31 | AAA030
+ (1242,42,foo,,,,"ft2       ",) | (1242,42,bar,,,,"ft2       ",) | (1242,42,bar,,,,"ft2       ",) | 1242 | 42 | bar |    |    |    | ft2        |    | (42,43,AAA042) | 42 | 43 | AAA042
+ (1248,48,foo,,,,"ft2       ",) | (1248,48,bar,,,,"ft2       ",) | (1248,48,bar,,,,"ft2       ",) | 1248 | 48 | bar |    |    |    | ft2        |    | (48,49,AAA048) | 48 | 49 | AAA048
+ (1260,60,foo,,,,"ft2       ",) | (1260,60,bar,,,,"ft2       ",) | (1260,60,bar,,,,"ft2       ",) | 1260 | 60 | bar |    |    |    | ft2        |    | (60,61,AAA060) | 60 | 61 | AAA060
+ (1266,66,foo,,,,"ft2       ",) | (1266,66,bar,,,,"ft2       ",) | (1266,66,bar,,,,"ft2       ",) | 1266 | 66 | bar |    |    |    | ft2        |    | (66,67,AAA066) | 66 | 67 | AAA066
+ (1278,78,foo,,,,"ft2       ",) | (1278,78,bar,,,,"ft2       ",) | (1278,78,bar,,,,"ft2       ",) | 1278 | 78 | bar |    |    |    | ft2        |    | (78,79,AAA078) | 78 | 79 | AAA078
+ (1284,84,foo,,,,"ft2       ",) | (1284,84,bar,,,,"ft2       ",) | (1284,84,bar,,,,"ft2       ",) | 1284 | 84 | bar |    |    |    | ft2        |    | (84,85,AAA084) | 84 | 85 | AAA084
+ (1296,96,foo,,,,"ft2       ",) | (1296,96,bar,,,,"ft2       ",) | (1296,96,bar,,,,"ft2       ",) | 1296 | 96 | bar |    |    |    | ft2        |    | (96,97,AAA096) | 96 | 97 | AAA096
+ (1218,18,foo,,,,"ft2       ",) | (1218,18,bar,,,,"ft2       ",) | (1218,18,bar,,,,"ft2       ",) | 1218 | 18 | bar |    |    |    | ft2        |    | (18,19,AAA018) | 18 | 19 | AAA018
+ (1236,36,foo,,,,"ft2       ",) | (1236,36,bar,,,,"ft2       ",) | (1236,36,bar,,,,"ft2       ",) | 1236 | 36 | bar |    |    |    | ft2        |    | (36,37,AAA036) | 36 | 37 | AAA036
+ (1254,54,foo,,,,"ft2       ",) | (1254,54,bar,,,,"ft2       ",) | (1254,54,bar,,,,"ft2       ",) | 1254 | 54 | bar |    |    |    | ft2        |    | (54,55,AAA054) | 54 | 55 | AAA054
+ (1272,72,foo,,,,"ft2       ",) | (1272,72,bar,,,,"ft2       ",) | (1272,72,bar,,,,"ft2       ",) | 1272 | 72 | bar |    |    |    | ft2        |    | (72,73,AAA072) | 72 | 73 | AAA072
+ (1290,90,foo,,,,"ft2       ",) | (1290,90,bar,,,,"ft2       ",) | (1290,90,bar,,,,"ft2       ",) | 1290 | 90 | bar |    |    |    | ft2        |    | (90,91,AAA090) | 90 | 91 | AAA090
+(16 rows)
+
+ROLLBACK;
 EXPLAIN (verbose, costs off)
 DELETE FROM ft2
   USING ft4 LEFT JOIN ft5 ON (ft4.c1 = ft5.c1)

contrib/postgres_fdw/sql/postgres_fdw.sql

@@ -1469,7 +1469,7 @@ EXPLAIN (verbose, costs off)
 INSERT INTO ft2 (c1,c2,c3) SELECT c1+1000,c2+100, c3 || c3 FROM ft2 LIMIT 20;
 INSERT INTO ft2 (c1,c2,c3) SELECT c1+1000,c2+100, c3 || c3 FROM ft2 LIMIT 20;
 INSERT INTO ft2 (c1,c2,c3)
-  VALUES (1101,201,'aaa'), (1102,202,'bbb'), (1103,203,'ccc') RETURNING *;
+  VALUES (1101,201,'aaa'), (1102,202,'bbb'), (1103,203,'ccc') RETURNING old, new, old.*, new.*;
 INSERT INTO ft2 (c1,c2,c3) VALUES (1104,204,'ddd'), (1105,205,'eee');
 EXPLAIN (verbose, costs off)
 UPDATE ft2 SET c2 = c2 + 300, c3 = c3 || '_update3' WHERE c1 % 10 = 3;              -- can be pushed down
@@ -1477,6 +1477,13 @@ UPDATE ft2 SET c2 = c2 + 300, c3 = c3 || '_update3' WHERE c1 % 10 = 3;
 EXPLAIN (verbose, costs off)
 UPDATE ft2 SET c2 = c2 + 400, c3 = c3 || '_update7' WHERE c1 % 10 = 7 RETURNING *;  -- can be pushed down
 UPDATE ft2 SET c2 = c2 + 400, c3 = c3 || '_update7' WHERE c1 % 10 = 7 RETURNING *;
+BEGIN;
+  EXPLAIN (verbose, costs off)
+  UPDATE ft2 SET c2 = c2 + 400, c3 = c3 || '_update7b' WHERE c1 % 10 = 7 AND c1 < 40
+    RETURNING old.*, new.*;                                                         -- can't be pushed down
+  UPDATE ft2 SET c2 = c2 + 400, c3 = c3 || '_update7b' WHERE c1 % 10 = 7 AND c1 < 40
+    RETURNING old.*, new.*;
+ROLLBACK;
 EXPLAIN (verbose, costs off)
 UPDATE ft2 SET c2 = ft2.c2 + 500, c3 = ft2.c3 || '_update9', c7 = DEFAULT
   FROM ft1 WHERE ft1.c1 = ft2.c2 AND ft1.c1 % 10 = 9;                               -- can be pushed down
@@ -1485,6 +1492,11 @@ UPDATE ft2 SET c2 = ft2.c2 + 500, c3 = ft2.c3 || '_update9', c7 = DEFAULT
 EXPLAIN (verbose, costs off)
   DELETE FROM ft2 WHERE c1 % 10 = 5 RETURNING c1, c4;                               -- can be pushed down
 DELETE FROM ft2 WHERE c1 % 10 = 5 RETURNING c1, c4;
+BEGIN;
+  EXPLAIN (verbose, costs off)
+  DELETE FROM ft2 WHERE c1 % 10 = 6 AND c1 < 40 RETURNING old.c1, c4;               -- can't be pushed down
+  DELETE FROM ft2 WHERE c1 % 10 = 6 AND c1 < 40 RETURNING old.c1, c4;
+ROLLBACK;
 EXPLAIN (verbose, costs off)
 DELETE FROM ft2 USING ft1 WHERE ft1.c1 = ft2.c2 AND ft1.c1 % 10 = 2;                -- can be pushed down
 DELETE FROM ft2 USING ft1 WHERE ft1.c1 = ft2.c2 AND ft1.c1 % 10 = 2;
@@ -1511,6 +1523,17 @@ UPDATE ft2 SET c3 = 'foo'
   FROM ft4 INNER JOIN ft5 ON (ft4.c1 = ft5.c1)
   WHERE ft2.c1 > 1200 AND ft2.c2 = ft4.c1
   RETURNING ft2, ft2.*, ft4, ft4.*;
+BEGIN;
+  EXPLAIN (verbose, costs off)
+  UPDATE ft2 SET c3 = 'bar'
+    FROM ft4 INNER JOIN ft5 ON (ft4.c1 = ft5.c1)
+    WHERE ft2.c1 > 1200 AND ft2.c2 = ft4.c1
+    RETURNING old, new, ft2, ft2.*, ft4, ft4.*;  -- can't be pushed down
+  UPDATE ft2 SET c3 = 'bar'
+    FROM ft4 INNER JOIN ft5 ON (ft4.c1 = ft5.c1)
+    WHERE ft2.c1 > 1200 AND ft2.c2 = ft4.c1
+    RETURNING old, new, ft2, ft2.*, ft4, ft4.*;
+ROLLBACK;
 EXPLAIN (verbose, costs off)
 DELETE FROM ft2
   USING ft4 LEFT JOIN ft5 ON (ft4.c1 = ft5.c1)