Re: [PATCH] Proposal for HIDDEN/INVISIBLE column

Le 14/10/2021 à 20:43, Tom Lane a écrit :
> Re-reading that, I realize I probably left way too much unstated,
> so let me spell it out.
>
> Should this feature affect
>     SELECT * FROM my_table t;
> ?  Yes, absolutely.
>
> How about
>     SELECT t.* FROM my_table t;
> ?  Yup, one would think so.
>
> Now how about
>     SELECT row_to_json(t.*) FROM my_table t;
> ?  All of a sudden, I'm a lot less sure --- not least because we *can't*
> simply omit some columns, without the composite datum suddenly not being
> of the table's rowtype anymore, which could have unexpected effects on
> query semantics.  In particular, if we have a user-defined function
> that's defined to accept composite type my_table, I don't think we can
> suppress columns in
>     SELECT myfunction(t.*) FROM my_table t;
>
> And don't forget that these can also be spelled like
>     SELECT row_to_json(t) FROM my_table t;
> without any star visible anywhere.
>
> So the more I think about this, the squishier it gets.  I'm now sharing
> the fears expressed upthread about whether it's even possible to define
> this in a way that won't have a lot of gotchas.
>
>             regards, tom lane


You mean this ? :-)


gilles=# CREATE TABLE htest0 (a int PRIMARY KEY, b text NOT NULL HIDDEN);
CREATE TABLE
gilles=# INSERT INTO htest0 (a, b) VALUES (1, 'htest0 one');
INSERT 0 1
gilles=# INSERT INTO htest0 (a, b) VALUES (2, 'htest0 two');
INSERT 0 1

gilles=# SELECT * FROM htest0 t;
  a
---
  1
  2
(2 rows)

gilles=# SELECT t.* FROM htest0 t;
  a
---
  1
  2
(2 rows)

gilles=# SELECT row_to_json(t.*) FROM htest0 t;
        row_to_json
--------------------------
  {"a":1,"b":"htest0 one"}
  {"a":2,"b":"htest0 two"}
(2 rows)

gilles=# SELECT row_to_json(t) FROM htest0 t;
        row_to_json
--------------------------
  {"a":1,"b":"htest0 one"}
  {"a":2,"b":"htest0 two"}
(2 rows)


You should have a look at the patch, I don't think that the way it is 
done there could have gotchas.

-- 
Gilles Darold