Re: Support logical replication of DDLs

> I applied patch 0005.
>
> I think this modification is a bit overdone.
> This design skips all subcommands, which results in many ddl
> replication failures.
> For example:
> ```
> CREATE TABLE datatype_table (id SERIAL);
> ```
> deparsed ddl is:
> CREATE TABLE public.datatype_table (id pg_catalog.int4 STORAGE plain
> NOT NULL DEFAULT
> pg_catalog.nextval('public.datatype_table_id_seq'::pg_catalog.regclass))
> CREATE SEQUENCE subcommand will be skipped.
>
> OR:
> ```
> CREATE SCHEMA element_test
> CREATE TABLE foo (id int)
> CREATE VIEW bar AS SELECT * FROM foo;
> ```
> deparsed ddl is:
> CREATE SCHEMA element_test.
>
> Its subcommands will be skipped.
> There may be other cases.
>
> For the initial CREATE LIKE statement, It is special,
> It derives the subcommand of alter table column.
> Just skipping them may be enough.
> Instead of skipping subcommands of all statements.
> After all, our design is to obtain the actual ddl information from the
> catalog instead of parsing raw parsetree.
> This is why we cannot skip all subcommands.

Agreed, event triggers capture commands on the subcommand level so
we can't skip subcommands at large without modifying how to
deparse top level commands such as CREATE TABLE/INDEX/SCHEMA.
Also for special statements like CREATE TABLE datatype_table (id SERIAL);
the CREATE SEQUENCE subcommand actually has to execute before
the top level command CREATE TABLE.

Attached please find a new solution that skips the deparsing of ALTER TABLE
subcommands generated for TableLikeClause. The patch v42-0005 added a new
boolean field table_like to AlterTableStmt in order to identify an ALTER TABLE
subcommand generated internally for the TableLikeClause.

Regards,
Zheng