我有这张桌子
+------------+------------+
| debt | credit |
+------------+------------+
| 10.00 | 0.00 |
| 0.00 | 10.00 |
| 20.00 | 0.00 |
| 10.00 | 0.00 |
| 0.00 | 5.00 |
| 0.00 | 2.00 |
| 10.00 | 0.00 |
| 0.00 | 25.00 |
| 100.00 | 0.000 |
+------------+------------+
我想通过这个表达式计算余额字段： balance =（债务信用）+余额
在我的报告rdlc
+------------+------------+---------+
| debt | credit | balance |
+------------+------------+---------+
| 10.00 | 0.00 | 10.00 |
| 0.00 | 10.00 | 0.00 |
| 20.00 | 0.00 | 20.00 |
| 10.00 | 0.00 | 30.00 |
| 0.00 | 5.00 | 25.00 |
| 0.00 | 2.00 | 23.00 |
| 10.00 | 0.00 | 33.00 |
| 0.00 | 25.00 | 8.00 |
| 100.00 | 0.000 |108.00 |
+------------+------------+---------+