Oracle Database Discussions

Hi All,
I am new to sql. I want to use decode for BLOB datatype. For this i written a query like below.
Here user_data is of type BLOB.

select DECODE(length(user_data), 0, null, file_data) user_data from user_table;

I have tried the other way by using case like below. Its worked fine

select
CASE
WHEN LENGTH(user_data )=0
THEN NULL
ELSE user_data
END user_data from user_table;

What i made wrong in the first query?


Thanks
Jimmi