Is this a bug? (about analytic function)

Question

create table emp (
empno varchar2(10),
deptno varchar2(10),
sal number(10)
insert into emp(empno,deptno,sal) values('1','10',101);
insert into emp(empno,deptno,sal) values('2','20',102);
insert into emp(empno,deptno,sal) values('3','20',103);
insert into emp(empno,deptno,sal) values('4','10',104);
insert into emp(empno,deptno,sal) values('5','30',105);
insert into emp(empno,deptno,sal) values('6','30',106);
insert into emp(empno,deptno,sal) values('7','30',107);
insert into emp(empno,deptno,sal) values('8','40',108);
insert into emp(empno,deptno,sal) values('9','30',109);
insert into emp(empno,deptno,sal) values('10','30',110);
insert into emp(empno,deptno,sal) values('11','30',100);
SELECT empno, deptno, sal,
last_value(sal)
OVER (PARTITION BY deptno order by sal desc) col1,
first_value(sal)
OVER (PARTITION BY deptno order by sal asc) col2,
first_value(sal)
OVER (PARTITION BY deptno order by sal desc) col3,
last_value(sal)
OVER (PARTITION BY deptno order by sal asc) col4
FROM emp
col2, col3 return what I expect.
I don't know why col1 and col4 return the these kinds of results.

Answer 1

Well... I learned something new today!
This is because you have not defined a windowing clause in your analytic query. If you do not specify a windowing clause, the default used is RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW. So your query is equivalent to:
  1  select empno, deptno, sal,
  2  last_value(sal) over (
  3     partition by deptno
  4     order by sal desc
  5     range between unbounded preceding and current row
  6  ) col1,
  7  first_value(sal) over (
  8     partition by deptno
  9     order by sal asc
10     range between unbounded preceding and current row
11  ) col2,
12  first_value(sal) over (
13     partition by deptno
14     order by sal desc
15     range between unbounded preceding and current row
16  ) col3,
17  last_value(sal) over (
18     partition by deptno
19     order by sal asc
20     range between unbounded preceding and current row
21  ) col4
22* from emp
SQL> /
     EMPNO     DEPTNO        SAL       COL1       COL2       COL3       COL4
         4         10        104        104        101        104        104
         1         10        101        101        101        104        101
         3         20        103        103        102        103        103
         2         20        102        102        102        103        102
        10         30        110        110        100        110        110
         9         30        109        109        100        110        109
         7         30        107        107        100        110        107
         6         30        106        106        100        110        106
         5         30        105        105        100        110        105
        11         30        100        100        100        110        100
        11         30        100        100        100        110        100
         8         40        108        108        108        108        108
12 rows selected.What you need to do is specify the correct windowing clause as follows:
  1  select empno, deptno, sal,
  2  last_value(sal) over (
  3     partition by deptno
  4     order by sal desc
  5     range between unbounded preceding and unbounded following
  6  ) col1,
  7  first_value(sal) over (
  8     partition by deptno
  9     order by sal asc
10  ) col2,
11  first_value(sal) over (
12     partition by deptno
13     order by sal desc
14  ) col3,
15  last_value(sal) over (
16     partition by deptno
17     order by sal asc
18     range between unbounded preceding and unbounded following
19  ) col4
20* from emp
SQL> /
     EMPNO     DEPTNO        SAL       COL1       COL2       COL3       COL4
         4         10        104        101        101        104        104
         1         10        101        101        101        104        104
         3         20        103        102        102        103        103
         2         20        102        102        102        103        103
        10         30        110        100        100        110        110
         9         30        109        100        100        110        110
         7         30        107        100        100        110        110
         6         30        106        100        100        110        110
         5         30        105        100        100        110        110
        11         30        100        100        100        110        110
        11         30        100        100        100        110        110
         8         40        108        108        108        108        108
12 rows selected....which gives the expected results. Or just use max(), which is clearer anyway :)
This is documented on Metalink, bug number 5684819:
"If you omit the windowing_clause of the analytic_clause, it defaults to RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW. This default will return a value that sometimes may seem unexpected, because the last value in the window is at the bottom of the window, which is not fixed. It keeps changing as the current row changes. For expected results, specify the windowing clause as RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING. Another option, is to specify the windowing clause as RANGE BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING."
cheers,
Anthony