Oracle 11g Release 2

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create table t(Id INT, Val varchar2(50));
INSERT INTO t(Id, Val)
SELECT 10, 'a' FROM dual
UNION ALL SELECT 20,'b' FROM dual
UNION ALL SELECT 30, 'a' FROM dual
UNION ALL SELECT 40,'b' FROM dual
4 rows affected

SELECT * FROM t;


ID
VAL


10
a

20
b

30
a

40
b


DECLARE
   l_cnt INT;
BEGIN
   DELETE FROM t RETURNING COUNT(val) INTO l_cnt;
   DBMS_OUTPUT.put_line('l_cnt: ' || l_cnt);
END;
//
1 rows affected

dbms_output:
l_cnt: 4

INSERT INTO t
SELECT 10, 'a' FROM dual
UNION ALL SELECT 20,'b' FROM dual
UNION ALL SELECT 30, 'a' FROM dual
UNION ALL SELECT 40,'b' FROM dual
4 rows affected

DECLARE
   l_cnt INT;
BEGIN
   DELETE FROM t RETURNING COUNT(DISTINCT val) INTO l_cnt;
   DBMS_OUTPUT.put_line('l_cnt: ' || l_cnt);
END;
//
ORA-00934: group function is not allowed here
ORA-06512: at line 4