How to dbms_output.put_line in Oracle - oracle

Question

The result doesn't show the command ROUND(SYSDATE - V_FECHA,1) by dbms_output.put_line, I have this script:
SET SERVEROUTPUT ON
DECLARE
v_fecha v$database.created%TYPE;
BEGIN
CASE
WHEN ( SYSDATE - v_fecha <= 50 ) THEN
dbms_output.put_line('LA FECHA DE CREACION DE LA BASE DE DATOS ES <= 50 DÍAS');
WHEN ( SYSDATE - v_fecha > 50 AND SYSDATE - v_fecha <= 100 ) THEN
dbms_output.put_line('LA FECHA DE CREACIÓN ES MAYOR QUE 50 DÍAS O <= 100 DÍAS');
ELSE
dbms_output.put_line('LA FECHA DE CREACIÓN ES IGUAL A '
|| round(SYSDATE - v_fecha,1)
|| ' DÍAS');
END CASE;
END;
/
OUTPUT:
LA FECHA DE CREACIÓN ES IGUAL A DÍAS.
Oracle Version: Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production
IDE: SQL DEVELOPER - Versión 4.1.1.19
Thanks.

Answer 1

The output of the command ROUND(SYSDATE - V_FECHA,1) is not shown, because V_FECHA is still NULL in your code. You can verify that with
SELECT ROUND(SYSDATE - NULL) FROM DUAL;
which doesn't show anything, too. Nearly every operation in SQL will output NULL if the input contains NULL values, and DBMS_OUTPUT shows then an empty string.
As #Kaushik suggested, if you add the SELECT to your code, and maybe something that catches NULL values, everything should be fine:
DECLARE
v_fecha v$database.created%TYPE;
delta NUMBER;
BEGIN
SELECT created INTO v_fecha FROM v$database;
delta := v_fecha - SYSDATE;
CASE WHEN delta <= 50 THEN
dbms_output.put_line('LA FECHA DE CREACION DE LA BASE DE DATOS ES <= 50 DÍAS');
WHEN delta > 50 AND delta <= 100 THEN
dbms_output.put_line('LA FECHA DE CREACIÓN ES MAYOR QUE 50 DÍAS O <= 100 DÍAS');
WHEN delta IS NULL THEN
dbms_output.put_line('LA FECHA DE CREACIÓN ES DESCONOCIDA');
ELSE
dbms_output.put_line('LA FECHA DE CREACIÓN ES IGUAL A '
|| NVL(round(SYSDATE - v_fecha,1), 0)
|| ' DÍAS');
END CASE;
END;
/
I put in two options, WHEN delta IS NULL and NVL to show you different possibilities.
Furthermore I try to call SYSDATE only once, as every call of SYSDATE might be slightly later than the previous one. (The difference is of course very little, but I am trying to prevent errors which occur very rarely but are then very difficult to find.)

Answer 2

You probably want to fetch from v$database. Add this after BEGIN
SELECT
created
INTO v_fecha
FROM
v$database;