DECLARE i testtable.text%TYPE; j testtable.text%TYPE; t testtable.text%TYPE;
BEGIN
    SELECT MIN(id) INTO i FROM testtable;
    SELECT MAX(id) INTO j FROM testtable;
    WHILE i<=j LOOP
        SELECT text INTO t FROM testtable WHERE id=i;
        UPDATE testtable SET text=(t||'_X') WHERE id=i;
        SELECT MIN(id) INTO i FROM testtable WHERE id>i;
    END LOOP;
END;