[#23011] YSQL: Enable ALTER TABLE IF EXISTS t RENAME c1 TO c2

Summary:
Enabled YSQL `ALTER TABLE IF EXISTS ... RENAME ... TO ...` syntax.
In fact the needed internal functionality was already implemented in the functions: `renameatt` and `YBCRename`,
but the command was disabled at the grammar level.

The diff also adds several test-cases for the syntax:
* `ALTER TABLE IF EXISTS ...` (new enabled functionality)
* `ALTER TABLE ... RENAME COLUMN ...`
* Plus minor changes for `ALTER TABLE ... RENAME ...`
Jira: DB-11940

Test Plan:
./yb_build.sh --java-test org.yb.pgsql.TestPgRegressFeature#testPgRegressFeature
./yb_build.sh --java-test org.yb.pgsql.TestPgRegressTable#testPgRegressTable

Reviewers: mihnea, fizaa, jason

Reviewed By: jason

Subscribers: jason, yql

Differential Revision: https://phorge.dev.yugabyte.com/D36390

src/postgres/src/backend/parser/gram.y

@@ -9665,7 +9665,6 @@ RenameStmt: ALTER AGGREGATE aggregate_with_argtypes RENAME TO name
 				}
 			| ALTER TABLE IF_P EXISTS relation_expr RENAME opt_column name TO name
 				{
-					parser_ybc_not_support(@1, "ALTER TABLE IF EXISTS");
 					RenameStmt *n = makeNode(RenameStmt);
 					n->renameType = OBJECT_COLUMN;
 					n->relationType = OBJECT_TABLE;

src/postgres/src/test/regress/expected/yb_feature_alter_table.out

@@ -253,7 +253,14 @@ ERROR:  constraint "checkb2" for table "atacc1" does not exist
 alter table atacc1 drop constraint if exists checkb3;
 delete from atacc1 where b = 5;
 -- test rename
-alter table atacc1 rename b to e;
+alter table atacc1 rename b to d; -- should fail: d already exists
+ERROR:  column "d" of relation "atacc1" already exists
+alter table atacc1 rename b to f;
+alter table atacc1 rename column f to e;
+alter table if exists doesnt_exist_tab rename b to f;
+NOTICE:  relation "doesnt_exist_tab" does not exist, skipping
+alter table if exists doesnt_exist_tab rename column f to e;
+NOTICE:  relation "doesnt_exist_tab" does not exist, skipping
 select * from atacc1;
  e  | c  | d
 ----+----+----

src/postgres/src/test/regress/expected/yb_pg_alter_table.out

@@ -292,6 +292,33 @@ Check constraints:
 
 DROP TABLE constraint_rename_cache;
 DROP TABLE like_constraint_rename_cache;
+-- test inheritance
+create table renameColumn (a int);
+create table renameColumnChild (b int) inherits (renameColumn);
+ERROR:  INHERITS not supported yet
+LINE 1: create table renameColumnChild (b int) inherits (renameColum...
+                                               ^
+HINT:  See https://github.com/yugabyte/yugabyte-db/issues/1129. React with thumbs up to raise its priority
+/* YB: uncomment when INHERITS is supported
+create table renameColumnAnother (c int) inherits (renameColumnChild);
+
+-- these three should fail
+alter table renameColumnChild rename column a to d;
+alter table only renameColumnChild rename column a to d;
+alter table only renameColumn rename column a to d;
+*/ -- YB
+-- these should work
+alter table renameColumn rename column a to d;
+/* YB: uncomment when INHERITS is supported
+alter table renameColumnChild rename column b to a;
+*/ -- YB
+-- these should work
+alter table if exists doesnt_exist_tab rename column a to d;
+NOTICE:  relation "doesnt_exist_tab" does not exist, skipping
+alter table if exists doesnt_exist_tab rename column b to a;
+NOTICE:  relation "doesnt_exist_tab" does not exist, skipping
+-- this should work
+alter table renameColumn add column w int;
 --
 -- lock levels
 --

src/postgres/src/test/regress/sql/yb_feature_alter_table.sql

@@ -144,7 +144,13 @@ alter table atacc1 drop constraint if exists checkb3;
 delete from atacc1 where b = 5;
 
 -- test rename
-alter table atacc1 rename b to e;
+alter table atacc1 rename b to d; -- should fail: d already exists
+alter table atacc1 rename b to f;
+alter table atacc1 rename column f to e;
+
+alter table if exists doesnt_exist_tab rename b to f;
+alter table if exists doesnt_exist_tab rename column f to e;
+
 select * from atacc1;
 
 -- try dropping all columns

src/postgres/src/test/regress/sql/yb_pg_alter_table.sql

@@ -297,6 +297,33 @@ CREATE TABLE like_constraint_rename_cache
 DROP TABLE constraint_rename_cache;
 DROP TABLE like_constraint_rename_cache;
 
+-- test inheritance
+
+create table renameColumn (a int);
+create table renameColumnChild (b int) inherits (renameColumn);
+/* YB: uncomment when INHERITS is supported
+create table renameColumnAnother (c int) inherits (renameColumnChild);
+
+-- these three should fail
+alter table renameColumnChild rename column a to d;
+alter table only renameColumnChild rename column a to d;
+alter table only renameColumn rename column a to d;
+*/ -- YB
+
+-- these should work
+alter table renameColumn rename column a to d;
+/* YB: uncomment when INHERITS is supported
+alter table renameColumnChild rename column b to a;
+*/ -- YB
+
+-- these should work
+alter table if exists doesnt_exist_tab rename column a to d;
+alter table if exists doesnt_exist_tab rename column b to a;
+
+-- this should work
+alter table renameColumn add column w int;
+
+
 --
 -- lock levels
 --