How to read custom table in Exit ?

Dear Experts,

I have a Z table with below fields.

Calender Date Merchandising Date

01/01/2008 30/12/2007

02/01/2008 31/12/2007

03/01/2008 01/01/2008

04/01/2008 02/01/2008

I need to calculate the YTD based on merchandising date.

Suppose, if the current system date is 04/01/2008, i need to calculate the merchandising YTD ( i.e sum of 01/01/2008 and 02/01/2008) based on above mapping table.

Can you pls help me with solution ?

Regards,

Srikanth