Function behaviour

CREATE temp TABLE msl09(c1 text, c2 text);
INSERT INTO msl09 VALUES ('123', '321');
INSERT INTO msl09 VALUES ('abcd', '321');
INSERT INTO msl09 VALUES ('abcdw', '321');
INSERT INTO msl09 VALUES('234', '4a66');
INSERT INTO msl09 VALUES('234', '466');

CREATE OR REPLACE FUNCTION test() RETURNS INTEGER AS $$
DELETE FROM msl09 WHERE c2 = (SELECT c2 FROM msl09 WHERE c1 = '123');
DELETE FROM msl09 WHERE c1 = (SELECT c2 FROM msl09);
SELECT 1;
$$ LANGUAGE SQL;

SELECT test();
SELECT * FROM msl09;