This function deletes all members of a specified derived set set_name, and is only available for use in calc sections. Note that @NULLSET does not currently work on primitive sets. But you can workaround this by creating a derived set directly from  a primitive set, and then null out this derived set. For example:

SETS:

  MYPRIMITIVESET1 /1..3/;

  MYDERIVEDSET( MYSET1);

ENDSETS

CALC:

  ! The following nulling of a primitive set is not allowed;

  @NULLSET( MYPRIMITIVESET);

 

  ! The next statement is allowed, given that we are nulling a derived set;

  @NULLSET( MYDERIVEDSET);

ENDCALC

Once a set is nulled, you will typically add selected members back using the @INSERT function.