NILADIC FUNCTIONS v7.0
Yes, "niladic" is actually a word. According to Dictionary.com, it is 
"a less common synonym for 'nullary,'" which in turn means "a 
description of an operator or function which takes no arguments."

SQL Server v7.0 supports a few niladic functions that were actually 
introduced in prior versions. Functionally, there is no difference 
between functions that accept parameters and those that do not. Though 
these functions are redundant, it helps to know what a niladic function 
is and what it does--a question that sometimes pops up during 
interviews to gauge how well an applicant knows the intricacies of SQL 
Server.

The following niladic functions have been supported in SQL Server since 
v6.0 but are now included to follow the ANSI 92 standard. Each niladic 
function is equated with a newer function that accepts arguments.

* USER equates to the USER_NAME() SQL Server v7.0 function.

* CURRENT_USER equates to the USER_NAME() SQL Server v7.0 function.

* SESSION_USER equates to the USER_NAME() SQL Server v7.0 function.

* SYSTEM_USER equates to the SUSER_NAME() SQL Server v7.0 function.

* CURRENT_TIMESTAMP equates to the GETDATE() SQL Server v7.0 function.

These functions can be used in a variety of places.

CREATE TABLE x( 
 DateEntered1 datetime NOT NULL CONSTRAINT df1 DEFAULT 
CURRENT_TIMESTAMP,  
 DateEntered2 datetime NOT NULL CONSTRAINT df2 DEFAULT 'GETDATE()' ) 
 
DECLARE @Sysuser1 varchar(20), 
        @Sysuser2 varchar(20) 
SET @Sysuser1 = SYSTEM_USER  
SET @Sysuser2 = SUSER_NAME()

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