DECLARE S VARCHAR2(25);
BEGIN
  FOR X IN (SELECT C_LOD FROM TBL WHERE C_TYPE = 'Такого значения нет в базе') LOOP
    S := X.DEV_NAME; -- ЗНАЧЕНИЕ БУДЕТ ТОЛЬКО ЕСЛИ ОНО ЕСТЬ
  END LOOP;
  DBMS_OUTPUT.PUT_LINE('S = '||S);
END;

DECLARE
    MyVar   DBA_EXTENTS.BYTES%TYPE;
    S VARCHAR2(256);
BEGIN
    S := '1. MyVar IS ' || MyVar;
    SELECT SUM(BYTES) INTO  MyVar FROM  DBA_EXTENTS WHERE OWNER = 'XXXX';
    S := S||' '||'2. SUM(BYTES) = '|| MyVar;
    SELECT NVL(SUM(BYTES),1) INTO  MyVar FROM  DBA_EXTENTS WHERE OWNER = 'XXXX';
    S := S||' '||'3. NVL(SUM(BYTES),1) = '|| MyVar;
    FOR X IN (SELECT BYTES  FROM  DBA_EXTENTS WHERE OWNER = 'XXXX') LOOP
       MyVar := X.BYTES;
       S := S||' СМОГЛИ ВЫБРАТЬ ХОТЬ ОДНУ СТРОКУ X.BYTES ='||MyVar;
    END LOOP;
    SELECT BYTES INTO  MyVar FROM  DBA_EXTENTS WHERE OWNER = 'XXXX';
    S:= S||' '||'4. SELECT BYTES =  '|| MyVar;
    DBMS_OUTPUT.PUT_LINE('S = '||S||'-> НОРМАЛЬНОЕ ЗАВЕРШЕНИЕ');
EXCEPTION  WHEN NO_DATA_FOUND THEN
        DBMS_OUTPUT.PUT_LINE('S = '||S||'->'||SQLERRM);
END;