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Thread: About the function current_user

About the function current_user

From

"Xiong He"

Date:

20 March 2023, 10:01:28

Dear All,

Just confused, why :

postgres=# select current_user;

current_user

--------------

postgres

(1 row)

postgres=# select current_user();

2023-03-20 07:00:02.981 UTC [17281] ERROR: syntax error at or near "(" at character 20

2023-03-20 07:00:02.981 UTC [17281] STATEMENT: select current_user();

ERROR: syntax error at or near "("

LINE 1: select current_user();

why current_user() is not recognized?

But the similar function current_database and current_database(), both can work.

Regards,

Xiong He [iihero]

Re: About the function current_user

From

Pavel Stehule

Date:

20 March 2023, 10:05:45

po 20. 3. 2023 v 8:01 odesílatel Xiong He <iihero@qq.com> napsal:

Dear All,

Just confused, why :
postgres=# select current_user;
current_user
--------------
postgres
(1 row)

postgres=# select current_user();
2023-03-20 07:00:02.981 UTC [17281] ERROR: syntax error at or near "(" at character 20
2023-03-20 07:00:02.981 UTC [17281] STATEMENT: select current_user();
ERROR: syntax error at or near "("
LINE 1: select current_user();
^

why current_user() is not recognized?

this is not real function - it is pseudo constant

The real function in postgres has a record in the pg_proc table.

Regards

Pavel

But the similar function current_database and current_database(), both can work.

Regards,
Xiong He [iihero]

Re: About the function current_user

From

Daniel Gustafsson

Date:

20 March 2023, 11:16:52

> On 20 Mar 2023, at 08:05, Pavel Stehule <pavel.stehule@gmail.com> wrote:
> po 20. 3. 2023 v 8:01 odesílatel Xiong He <iihero@qq.com <mailto:iihero@qq.com>> napsal:

> why current_user() is not recognized?
>
> this is not real function - it is pseudo constant
>
> The real function in postgres has a record in the pg_proc table.

The syntax of current_user and current_role are mandated by the SQL
specification, we have this note in the documentation:

    "current_catalog, current_role, current_schema, current_user,
    session_user, and user have special syntactic status in SQL: they must
    be called without trailing parentheses.  In PostgreSQL, parentheses can
    optionally be used with current_schema, but not with the others."

Given that current_schema and other current_xx functions accept parenthesis
it's easy to understand the confusion though.

--
Daniel Gustafsson

Re: About the function current_user

From

John Naylor

Date:

20 March 2023, 11:49:55

On Mon, Mar 20, 2023 at 3:16 PM Daniel Gustafsson <daniel@yesql.se> wrote:

> The syntax of current_user and current_role are mandated by the SQL
> specification, we have this note in the documentation:
>
> "current_catalog, current_role, current_schema, current_user,
> session_user, and user have special syntactic status in SQL: they must
> be called without trailing parentheses. In PostgreSQL, parentheses can
> optionally be used with current_schema, but not with the others."

To further illuminate why the last one is special: It's not a fully-reserved keyword:

$ grep current_ src/include/parser/kwlist.h
PG_KEYWORD("current_catalog", CURRENT_CATALOG, RESERVED_KEYWORD, BARE_LABEL)
PG_KEYWORD("current_date", CURRENT_DATE, RESERVED_KEYWORD, BARE_LABEL)
PG_KEYWORD("current_role", CURRENT_ROLE, RESERVED_KEYWORD, BARE_LABEL)
PG_KEYWORD("current_schema", CURRENT_SCHEMA, TYPE_FUNC_NAME_KEYWORD, BARE_LABEL)
PG_KEYWORD("current_time", CURRENT_TIME, RESERVED_KEYWORD, BARE_LABEL)
PG_KEYWORD("current_timestamp", CURRENT_TIMESTAMP, RESERVED_KEYWORD, BARE_LABEL)
PG_KEYWORD("current_user", CURRENT_USER, RESERVED_KEYWORD, BARE_LABEL)

--
John Naylor
EDB: http://www.enterprisedb.com

Re: About the function current_user

From

"Xiong He"

Date:

20 March 2023, 11:56:44

Thanks a lot.

And how to understand below result?

postgres=# select current_database();

current_database

------------------

postgres

(1 row)

postgres=# select current_database;

ERROR: column "current_database" does not exist

LINE 1: select current_database;

------------------ Original ------------------

From: "Daniel Gustafsson" <daniel@yesql.se>;

Date: Mon, Mar 20, 2023 04:16 PM

To: "Pavel Stehule"<pavel.stehule@gmail.com>;

Cc: "Xiong He"<iihero@qq.com>;"pgsql-bugs"<pgsql-bugs@lists.postgresql.org>;

Subject: Re: About the function current_user

> On 20 Mar 2023, at 08:05, Pavel Stehule <pavel.stehule@gmail.com> wrote:
> po 20. 3. 2023 v 8:01 odesílatel Xiong He <iihero@qq.com <mailto:iihero@qq.com>> napsal:

> why current_user() is not recognized?
>
> this is not real function - it is pseudo constant
>
> The real function in postgres has a record in the pg_proc table.

The syntax of current_user and current_role are mandated by the SQL
specification, we have this note in the documentation:

"current_catalog, current_role, current_schema, current_user,
session_user, and user have special syntactic status in SQL: they must
be called without trailing parentheses. In PostgreSQL, parentheses can
optionally be used with current_schema, but not with the others."

Given that current_schema and other current_xx functions accept parenthesis
it's easy to understand the confusion though.

--
Daniel Gustafsson

Re: About the function current_user

From

"Xiong He"

Date:

20 March 2023, 12:35:29

Great. So if it's in the PG_KEYWORD list, we should not use current_*()?

------------------ Original ------------------

From: "John Naylor" <john.naylor@enterprisedb.com>;

Date: Mon, Mar 20, 2023 04:49 PM

To: "Daniel Gustafsson"<daniel@yesql.se>;

Cc: "Pavel Stehule"<pavel.stehule@gmail.com>;"Xiong He"<iihero@qq.com>;"pgsql-bugs"<pgsql-bugs@lists.postgresql.org>;

Subject: Re: About the function current_user

Re: About the function current_user

From

John Naylor

Date:

20 March 2023, 15:13:48

On Mon, Mar 20, 2023 at 4:35 PM Xiong He <iihero@qq.com> wrote:
>
> Great. So if it's in the PG_KEYWORD list, we should not use current_*()?

That was just an explanation, regarding "reserved keywords", since you asked "why".

The documentation should have the correct uses. If it does, there is no bug here.

Speaking of bugs, I was wondering why appendix C didn't show up when searching within the doc website -- it's because the heading in appendix C spells it "key words", a spelling which seems non-standard and gets interpreted as "keywords" in a web search.

--
John Naylor
EDB: http://www.enterprisedb.com

Re: About the function current_user

From

John Naylor

Date:

20 March 2023, 15:16:58

On Mon, Mar 20, 2023 at 3:57 PM Xiong He <iihero@qq.com> wrote:
>
> Thanks a lot.
> And how to understand below result?
>
> postgres=# select current_database();
> current_database
> ------------------
> postgres
> (1 row)
>
> postgres=# select current_database;
> ERROR: column "current_database" does not exist
> LINE 1: select current_database;

"current_database" is not a keyword.

--
John Naylor
EDB: http://www.enterprisedb.com

Re: About the function current_user

From

Peter Eisentraut

Date:

20 March 2023, 16:58:38

On 20.03.23 13:13, John Naylor wrote:
> Speaking of bugs, I was wondering why appendix C didn't show up when 
> searching within the doc website -- it's because the heading in appendix 
> C spells it "key words", a spelling which seems non-standard and gets 
> interpreted as "keywords" in a web search.

The reason for that is that the SQL standard uses mainly "key word". 
But it's also somewhat inconsistent about that.