how two subreport connect to match on rows?

Hi,

I am using SSRS 2008 for my report. I am new to subreport. I have main report which will have two subreports. For main report, there will be each customer from master table; for one subreport, it will be data from detail report and group by year of phurchasing; for another subreport, it will be data from detail and group by each customer and phurchasing date.

The report will be like this:

                       C1        C2   C3      C4

01/2012        12.3      0      5.6     100.4

02/2012         0          0       2.8     3.6

...                     ...

12/2012        0           0       0        0

When view the report, the month of customer phurchasing amount not match the month of year from first column. How can I get them matched. And if amount is 0, the subreport not show 0, only shows nothing. How can I solve this problem?

Any suggestion will be appreciated.

Thanks