SQL & PL/SQL

Hi guys,

Oracle 11.2

I just found this by chance:

SQL> create table tab_0417(fid number, fdate date);

Table created

SQL> insert into tab_0417 values(1, date'2012-01-01');

1 row inserted

SQL> insert into tab_0417 values(1, NULL);

1 row inserted

SQL> commit;

Commit complete

SQL> select fid, fdate, nvl2(fdate, sysdate-fdate, sysdate) from tab_0417;

       FID FDATE       NVL2(FDATE,SYSDATE-FDATE,SYSDA
---------- ----------- ------------------------------
         1 1/1/2012                  107.580358796296
         1                            2456035.5803588

I expected an exception since the second and the third parameter of NVL2 have different data types and cannot be converted implicitly. But it executed successfully, and got a strange number 2456035.5803588, could anyone explain it?

Thanks in advance.