Código Delphi [-]
With IbScrip Do Begin
  With Sql Do Begin
    Clear;  
    Add('SET TERM ^ ;');
    Add('CREATE PROCEDURE "Art disponible" (');
    Add('    "Id inventario" BIGINT)');
    Add('RETURNS (');
    Add('    "Disponibles" DOUBLE PRECISION)');
    Add('AS');
    Add('DECLARE VARIABLE E DOUBLE PRECISION;');
    Add('DECLARE VARIABLE R DOUBLE PRECISION;');
    Add('begin');
    Add('  Select "Existencia" From "Inventario" Where "Id" = : "Id" "inventario" Into  : "E";');
    Add('  If ("E" is Null) Then');
    Add('    "E" = 0;');
    Add('  Select Sum("Cantidad") From "Reservados" Where "Id inventario"   = : "Id inventario" Into : "R";');
    Add('  If ("R" is Null) Then');
    Add('    "R" = 0;');
    Add('  "Disponibles" = : "E" - : "R";');
    Add('  suspend;');
    Add('end^');
    Add('SET TERM ; ^');
  End;
  Execute;
End;