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Is Oracle's CURRENT_TIMESTAMP function really a function?

I was under the impression that functions without arguments can be called with empty parentheses after the function name, that is, as some other databases allow:

current_timestamp()

While in Oracle I have to write

current_timestamp

This rule does not apply with custom functions (in 11g). I can write both

my_function
my_function()

My question is: Is the CURRENT_TIMESTAMP

function really a true function or should I think of it in the construct / pseudo-column language of the Oracle SQL dialect (SQL standard compliant)? Is there any formal definition of when I can (optionally, by mandate) add ()

and when I should omit them?

Background information:

  • SQL 1992 defines:

    <current timestamp value function> ::=
  CURRENT_TIMESTAMP [ <left paren> <timestamp precision> <right paren> ]

  • Derby, HSQLDB, Ingres, Postgres, SQLite, SQL Server behave like Oracle with no parentheses for CURRENT_TIMESTAMP

  • Sybase SQL Anywhere knows the function CURRENT TIMESTAMP

    (no parentheses, no underscore)
  • CUBRID, MySQL, Sybase ASE allow you to use CURRENT_TIMESTAMP()

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SQL standards since 1992 refer to CURRENT_TIMESTAMP as both a "time-varying system variable" and a "datetime value function". See, for example, SQL Database Language .

But AFAIK the standards always use CURRENT_TIMESTAMP, never CURRENT_TIMESTAMP (). Using CURRENT_TIMESTAMP () on compatible dbms should fail with a syntax error.



I'm not sure what the standards have to say about custom functions.

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