select md5 result set

Hi

I'm attempting to emulate feature available in Oracle, namely dbs_sqlhash.
For example, given the following table data values:

SQL> select x,y from test1;

X Y
---------- --------------------
5 White
1 YYY
2 Goodbye
6 Black

I can create a single hash value over the entire result set, specifically
md5, in a query as follows:

SQL> select dbms_sqlhash.gethash('select x,y from test1',2) as md5_value
from dual;

MD5_VALUE
--------------------------------------------------------------------------------
9FDA7FA725B783172CA371DA04AD5754

Can I do something similar in PostgreSQL ?

Thanks
P