Fix CREATE TABLE LIKE INCLUDING GENERATED column order issue

CREATE TABLE LIKE INCLUDING GENERATED would fail if a generated column
referred to a column with a higher attribute number.  This is because
the column mapping mechanism created the mapping incrementally as
columns are added.  This was sufficient for previous uses of that
mechanism (omitting dropped columns), and it also happened to work if
generated columns only referred to columns with lower attribute
numbers, but here it failed.

This fix is to build the attribute mapping in a separate loop before
processing the columns in detail.

Bug: #16342
Reported-by: Ethan Waldo <ewaldo@healthetechs.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>

src/backend/parser/parse_utilcmd.c

@@ -924,6 +924,7 @@ static void
 transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_clause)
 {
 	AttrNumber	parent_attno;
+	AttrNumber	new_attno;
 	Relation	relation;
 	TupleDesc	tupleDesc;
 	TupleConstr *constr;
@@ -986,6 +987,26 @@ transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_cla
 	 */
 	attmap = make_attrmap(tupleDesc->natts);
 
+	/*
+	 * We must fill the attmap now so that it can be used to process generated
+	 * column default expressions in the per-column loop below.
+	*/
+	new_attno = 1;
+	for (parent_attno = 1; parent_attno <= tupleDesc->natts;
+		 parent_attno++)
+	{
+		Form_pg_attribute attribute = TupleDescAttr(tupleDesc,
+													parent_attno - 1);
+
+		/*
+		 * Ignore dropped columns in the parent.  attmap entry is left zero.
+		 */
+		if (attribute->attisdropped)
+			continue;
+
+		attmap->attnums[parent_attno - 1] = list_length(cxt->columns) + (new_attno++);
+	}
+
 	/*
 	 * Insert the copied attributes into the cxt for the new table definition.
 	 */
@@ -998,7 +1019,7 @@ transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_cla
 		ColumnDef  *def;
 
 		/*
-		 * Ignore dropped columns in the parent.  attmap entry is left zero.
+		 * Ignore dropped columns in the parent.
 		 */
 		if (attribute->attisdropped)
 			continue;
@@ -1030,8 +1051,6 @@ transformTableLikeClause(CreateStmtContext *cxt, TableLikeClause *table_like_cla
 		 */
 		cxt->columns = lappend(cxt->columns, def);
 
-		attmap->attnums[parent_attno - 1] = list_length(cxt->columns);
-
 		/*
 		 * Copy default, if present and it should be copied.  We have separate
 		 * options for plain default expressions and GENERATED defaults.

src/test/regress/expected/create_table_like.out

@@ -159,14 +159,15 @@ SELECT * FROM test_like_gen_3;
 (1 row)
 
 DROP TABLE test_like_gen_1, test_like_gen_2, test_like_gen_3;
-CREATE TABLE test_like_4 (a int, b int DEFAULT 42, c int GENERATED ALWAYS AS (a * 2) STORED);
+-- also test generated column with a "forward" reference (bug #16342)
+CREATE TABLE test_like_4 (b int DEFAULT 42, c int GENERATED ALWAYS AS (a * 2) STORED, a int);
 \d test_like_4
                           Table "public.test_like_4"
  Column |  Type   | Collation | Nullable |              Default               
 --------+---------+-----------+----------+------------------------------------
- a      | integer |           |          | 
  b      | integer |           |          | 42
  c      | integer |           |          | generated always as (a * 2) stored
+ a      | integer |           |          | 
 
 CREATE TABLE test_like_4a (LIKE test_like_4);
 CREATE TABLE test_like_4b (LIKE test_like_4 INCLUDING DEFAULTS);
@@ -176,12 +177,12 @@ CREATE TABLE test_like_4d (LIKE test_like_4 INCLUDING DEFAULTS INCLUDING GENERAT
             Table "public.test_like_4a"
  Column |  Type   | Collation | Nullable | Default 
 --------+---------+-----------+----------+---------
- a      | integer |           |          | 
  b      | integer |           |          | 
  c      | integer |           |          | 
+ a      | integer |           |          | 
 
-INSERT INTO test_like_4a VALUES(11);
-TABLE test_like_4a;
+INSERT INTO test_like_4a (a) VALUES(11);
+SELECT a, b, c FROM test_like_4a;
  a  | b | c 
 ----+---+---
  11 |   |  
@@ -191,12 +192,12 @@ TABLE test_like_4a;
             Table "public.test_like_4b"
  Column |  Type   | Collation | Nullable | Default 
 --------+---------+-----------+----------+---------
- a      | integer |           |          | 
  b      | integer |           |          | 42
  c      | integer |           |          | 
+ a      | integer |           |          | 
 
-INSERT INTO test_like_4b VALUES(11);
-TABLE test_like_4b;
+INSERT INTO test_like_4b (a) VALUES(11);
+SELECT a, b, c FROM test_like_4b;
  a  | b  | c 
 ----+----+---
  11 | 42 |  
@@ -206,12 +207,12 @@ TABLE test_like_4b;
                          Table "public.test_like_4c"
  Column |  Type   | Collation | Nullable |              Default               
 --------+---------+-----------+----------+------------------------------------
- a      | integer |           |          | 
  b      | integer |           |          | 
  c      | integer |           |          | generated always as (a * 2) stored
+ a      | integer |           |          | 
 
-INSERT INTO test_like_4c VALUES(11);
-TABLE test_like_4c;
+INSERT INTO test_like_4c (a) VALUES(11);
+SELECT a, b, c FROM test_like_4c;
  a  | b | c  
 ----+---+----
  11 |   | 22
@@ -221,12 +222,12 @@ TABLE test_like_4c;
                          Table "public.test_like_4d"
  Column |  Type   | Collation | Nullable |              Default               
 --------+---------+-----------+----------+------------------------------------
- a      | integer |           |          | 
  b      | integer |           |          | 42
  c      | integer |           |          | generated always as (a * 2) stored
+ a      | integer |           |          | 
 
-INSERT INTO test_like_4d VALUES(11);
-TABLE test_like_4d;
+INSERT INTO test_like_4d (a) VALUES(11);
+SELECT a, b, c FROM test_like_4d;
  a  | b  | c  
 ----+----+----
  11 | 42 | 22

src/test/regress/sql/create_table_like.sql

@@ -65,24 +65,25 @@ INSERT INTO test_like_gen_3 (a) VALUES (1);
 SELECT * FROM test_like_gen_3;
 DROP TABLE test_like_gen_1, test_like_gen_2, test_like_gen_3;
 
-CREATE TABLE test_like_4 (a int, b int DEFAULT 42, c int GENERATED ALWAYS AS (a * 2) STORED);
+-- also test generated column with a "forward" reference (bug #16342)
+CREATE TABLE test_like_4 (b int DEFAULT 42, c int GENERATED ALWAYS AS (a * 2) STORED, a int);
 \d test_like_4
 CREATE TABLE test_like_4a (LIKE test_like_4);
 CREATE TABLE test_like_4b (LIKE test_like_4 INCLUDING DEFAULTS);
 CREATE TABLE test_like_4c (LIKE test_like_4 INCLUDING GENERATED);
 CREATE TABLE test_like_4d (LIKE test_like_4 INCLUDING DEFAULTS INCLUDING GENERATED);
 \d test_like_4a
-INSERT INTO test_like_4a VALUES(11);
-TABLE test_like_4a;
+INSERT INTO test_like_4a (a) VALUES(11);
+SELECT a, b, c FROM test_like_4a;
 \d test_like_4b
-INSERT INTO test_like_4b VALUES(11);
-TABLE test_like_4b;
+INSERT INTO test_like_4b (a) VALUES(11);
+SELECT a, b, c FROM test_like_4b;
 \d test_like_4c
-INSERT INTO test_like_4c VALUES(11);
-TABLE test_like_4c;
+INSERT INTO test_like_4c (a) VALUES(11);
+SELECT a, b, c FROM test_like_4c;
 \d test_like_4d
-INSERT INTO test_like_4d VALUES(11);
-TABLE test_like_4d;
+INSERT INTO test_like_4d (a) VALUES(11);
+SELECT a, b, c FROM test_like_4d;
 DROP TABLE test_like_4, test_like_4a, test_like_4b, test_like_4c, test_like_4d;
 
 CREATE TABLE inhg (x text, LIKE inhx INCLUDING INDEXES, y text); /* copies indexes */