Advanced sql with windowing claus

SELECT a.*,
       SUM(s.amount) over(ORDER BY s.month rows unbounded preceding) AS a ,
       SUM(s.amount) over(PARTITION BY s.month ORDER BY s.month rows unbounded preceding) AS b,
       SUM(s.amount) over(PARTITION BY s.month ) AS c_1,
       SUM(s.amount) over(PARTITION BY s.month ORDER BY s.month rows BETWEEN unbounded preceding AND unbounded following) AS c,
       SUM(s.amount) over(PARTITION BY s.month ORDER BY s.month rows BETWEEN 1 preceding AND unbounded following) AS d,
       SUM(s.amount) over(PARTITION BY s.month ORDER BY s.month rows BETWEEN 1 preceding AND 1 following) AS e,
       SUM(s.amount) over(PARTITION BY s.month ORDER BY s.month rows BETWEEN unbounded preceding AND 1 following) AS f,
       SUM(s.amount) over(PARTITION BY s.month ORDER BY s.month rows CURRENT ROW) AS g
  FROM all_sales s,
       (SELECT *
      FROM all_sales) a
 WHERE s.rowid = a.rowid;

/ --above query give the result shown below what is difference between c_1 and c column.

    YEAR  MONTH PRD_TYPE_ID EMP_ID  AMOUNT  A   B   C_1 C   D   E   F   G
1   2006    1   1             21    1.00    1   1   10  10  10  3   3   1
2   2006    1   1             21    2.00    3   3   10  10  10  6   6   2
3   2005    1   2             21    3.00    6   6   10  10  9   9   10  3
4   2005    1   2             22    4.00    10  10  10  10  7   7   10  4
5   2006    2   1             21    5.00    15  5   11  11  11  11  11  5
6   2005    2   1             21    6.00    21  11  11  11  11  11  11  6
7   2005    3   1             21            21      7   7   7   7   7   
8   2006    3   2             21    7.00    28  7   7   7   7   7   7   7
9   2005    4   1             21    8.00    36  8   17  17  17  17  17  8
10  2006    4   2             21    9.00    45  17  17  17  17  17  17  9
11  2006    5   2             21            45      10  10  10  10  10  
12  2005    5   1             21    10.00   55  10  10  10  10  10  10  10
13  2006    6   1             21    11.00   66  11  23  23  23  23  23  11
14  2005    6   1             21    12.00   78  23  23  23  23  23  23  12
15  2005    7   2             21    13.00   91  13  27  27  27  27  27  13
16  2006    7   1             21    14.00   105 27  27  27  27  27  27  14
17  2005    8   2             21    15.00   120 15  31  31  31  31  31  15
18  2006    8   1             21    16.00   136 31  31  31  31  31  31  16
19  2005    9   2             21    17.00   153 17  35  35  35  35  35  17
20  2006    9   1             21    18.00   171 35  35  35  35  35  35  18
21  2005    10  2             21    19.00   190 19  39  39  39  39  39  19
22  2006    10  1             21    20.00   210 39  39  39  39  39  39  20
23  2006    11  1             21    21.00   231 21  43  43  43  43  43  21
24  2005    11  1             21    22.00   253 43  43  43  43  43  43  22
25  2006    12  2             21    23.00   276 23  47  47  47  47  47  23
26  2005    12  1             21    24.00   300 47  47  47  47  47  47  24