An Empty String is Null in Oracle

(I ran this SQL in an Oracle 11 database.) Oracle treats an empty string as null. The length of an empty string is also null, not zero:

 

SQL> select nvl('','NULL1') null1 from dual;

 

NULL1

-----

NULL1

 

SQL> select nvl(to_char(length('')),'NULL2')

  2  null2 from dual;

 

NULL2

-----

NULL2

 

SQL>

This surprised me a little so I checked it a different way but got the same answer:

 

SQL> select 'Empty string is null'

  2  from dual

  3  where '' is null;

 

'EMPTYSTRINGISNULL'

--------------------

Empty string is null

 

SQL> select 'Empty string is not null'

  2  from dual

  3  where '' is not null;

 

no rows selected

 

SQL>