Meaning of 'SET' in error message 'Null value is eliminated by an aggregate or other SET operation'
I was just looking through the SQL-92 Specification and saw a passage that reminded me of this question.

There is in fact a prescribed warning for this situation as indicated below


  b) Otherwise, let TX be the single-column table that is the
                result of applying the &lt;value expression&gt; to each row of T
                and eliminating null values. If one or more null values are
                eliminated, then a completion condition is raised: warning-
                null value eliminated in set function.


I assume that the SET in the SQL Server Error Message is a reference to the set function of that error message although I'm not sure why it would make a distinction between aggregates and other set functions, as far as I can see they are synonymous. The relevant bit of the grammar is below.

6.5  &lt;set function specification&gt;

         Function

         Specify a value derived by the application of a function to an
         argument.

         Format

         &lt;set function specification&gt; ::=
                COUNT &lt;left paren&gt; &lt;asterisk&gt; &lt;right paren&gt;
              | &lt;general set function&gt;

         &lt;general set function&gt; ::=
                &lt;set function type&gt;
                    &lt;left paren&gt; [ &lt;set quantifier&gt; ] &lt;value expression&gt; &lt;right paren&gt;


         &lt;set function type&gt; ::=
              AVG | MAX | MIN | SUM | COUNT

         &lt;set quantifier&gt; ::= DISTINCT | ALL