Postgresql only selects the last row of the table for the list of values

At the example we have the table

CREATE TABLE IF NOT EXISTS t1 (a BYTEA NOT NULL,
r_pointer BIGINT,
s_pointer BIGINT,
BYTEA data,
PRIMARY KEY (a, r_pointer))
PARTITION BY HASH (a);

In case we want to get the last item:

SELECT * FROM t1 WHERE a = & # 39;  xaaa & # 39; command by r_pointer desc limit 1;

Of course, I can use executemany for this statement, but it's not very good for performance

How can I get only the first result found for each passing list { xaaa, xbbbb} to query in the following way:

SELECT * FROM t1 WHERE a = ANY (& # 39; { xaaa,  xbbbb} & # 39; :: bytea[])
order by r_pointer desc;

Thank you