Column aggregation in Oracle

Suppose we have a table (TBL) in Oracle with columns (CATEGORY, ATTR). Consider the following:

CATEGORY	ATTR
1	A
1	B
1	C
2	D
2	E
2	F
3	X
3	Y
3	Z

We want to convert the table as follows:

CATEGORY	ATTR
1	A,B,C
2	D,E,F
3	X,Y,Z

This can be done via the SQL below:

select CATEGORY, 
       xmlagg(xmlelement(c, ATTR || ',')).extract('//text()') 
from TBL 
group by CATEGORY