[feature]COPY FROM enable FORCE_NULL/FORCE_NOT_NULL on all columns

Hi,

The previous discussion is:

https://www.postgresql.org/message-id/CACJufxEnVqzOFtqhexF2%2BAwOKFrV8zHOY3y%3Dp%2BgPK6eB14pn_w%40mail.gmail.com

We  have FORCE_NULL/FORCE_NOT_NULL options when COPY FROM,  but users must set the columns one by one.

 CREATE TABLE forcetest (
 a INT NOT NULL,
 b TEXT NOT NULL,
 c TEXT,
 d TEXT,
 e TEXT
 );
 \pset null NULL

 BEGIN;
 COPY forcetest (a, b, c, d) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL(c,d), FORCE_NULL(c,d));
 1,'a',,""
 \.
 COMMIT;

 SELECT c, d FROM forcetest WHERE a = 1;
 c | d
 ---+------
 | NULL
 (1 row)

We don’t have  FORCE_NULL * or FORCE_NOT_NULL * for all columns of a table like FORCE_QUOTE *.

They should be helpful if a table have many columns.

This  patch enables FORCE_NULL/FORCE_NOT_NULL options to select all columns of a table  just like FORCE_QUOTE * (quote all columns).

 BEGIN
 COPY forcetest (a, b, c, d) FROM STDIN WITH (FORMAT csv, FORCE_NOT_NULL *, FORCE_NULL *);
 2,'b',,""
 \.
 COMMIT;

 SELECT c, d FROM forcetest WHERE a = 2;
 c | d
 ---+------
 | NULL
 (1 row)

Any thoughts?

Regards,
Zhang Mingli