Firebird Verificar Quebra de Sequencia

VERIFIY_SEQ.sql

/** 
* CREATING PROCEDURE TO CHECK
* NUMBERING BETWEEN SEQUENCE
**/
CREATE OR ALTER PROCEDURE VERIFY_SEQ (
	nMin INTEGER,
	nMax INTEGER
) RETURNS (n INTEGER)
AS
BEGIN
   n = nMin;
   while (n <= nMax) do
   BEGIN
      suspend;
      n = n+1;
   END
END

-- HOW TO USE
SELECT a.number
FROM VERIFY_SEQ( 200, 500 ) a
WHERE not exists (SELECT doc_number FROM docs b 
                    WHERE b.doc_number = a.numero
                    AND b.doc_number BETWEEN 200 AND 500)