Re: [HACKERS] proposal: schema variables

On 12.03.2018 09:54, Pavel Stehule wrote:
>
> 2018-03-12 7:49 GMT+01:00 Pavel Luzanov <p(dot)luzanov(at)postgrespro(dot)ru
> <mailto:p(dot)luzanov(at)postgrespro(dot)ru>>:
>
>
> Is there any chances that it will work on replicas?
>
> ...
>
> sure, it should to work. Now, I am try to solve a issues on concept
> level - the LET code is based on DML code base, so probably there is
> check for rw transactions. But it is useless for LET command.

Very, very good!

As I understand, the work on this patch now in progress and it not in
commitfest.
Please explain what features of schema variables I can review now.

From first post of this thread the syntax of the CREATE VARIABLE command:
CREATE [TEMP] VARIABLE [IF NOT EXISTS] name AS type
  [ DEFAULT expression ] [[NOT] NULL]
  [ ON TRANSACTION END { RESET | DROP } ]
  [ { VOLATILE | STABLE } ];

But in psql I see only:
\h create variable
Command:     CREATE VARIABLE
Description: define a new permissioned typed schema variable
Syntax:
CREATE VARIABLE [ IF NOT EXISTS ] name [ AS ] data_type ]

I can include DEFAULT clause in CREATE VARIABLE command, but the value
not used:
postgres=# create variable i int default 0;
CREATE VARIABLE
postgres=# select i;
 i
---

(1 row)

postgres=# \d+ i
 schema variable "public.i"
 Column |  Type   | Storage
--------+---------+---------
 i      | integer | plain

BTW, I found an error in handling of table aliases:

postgres=# create variable x text;
CREATE VARIABLE
postgres=# select * from pg_class AS x where x.relname = 'x';
ERROR:  type text is not composite

It thinks that x.relname is an attribute of x variable instead of an
alias for pg_class table.

-----
Pavel Luzanov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company