Hi Karthik,
how your report should look like from JAN to FEB and then FEB to MARCH
or else from JAN to MAR. Here in your code you have mentioned like
L_S_RANGE-LOW = LV_PREMONTH which contains value as JAN and
as L_S_RANGE_HIGH = LV_CURRMONTH which has the value FEB
If the user entry value is in the month of FEB. And in the next statement in your code is
L_S_RANGE-LOW = LV_CURRMONTH which has the value of FEB i.e means workarea - low has been overwrite with FEB previously it was JAN. So now the data appended to the E_T_DATA Table will from FEB to MARCH.
As said by Leo you can also do it in Bex by using the selections if you want your month data to be in 3 Different columns.See the last reply of LEO .
OR else give a try the code which i have given.
Hope this may help you.