i have the data in my table as follows,

```
+----+-----+
| ID | Qty |
+----+-----+
|  1 | 100 |
|  2 | 200 |
|  3 | 150 |
|  4 |  50 |
+----+-----+
```

i need the result as follows,

```
+----+-----+-------+
| ID | Qty | C.Qty |
+----+-----+-------+
|  1 | 100 |   100 |
|  2 | 200 |   300 |
|  3 | 150 |   450 |
|  4 |  50 |   500 |
+----+-----+-------+
```

the result of third column will be the sum of previous rows,
please any one help....