Internal table, BDC

Hello Friends,

i have to upload data into MD61. for that i will upload 'N' number of months. number of months will be given on the selection screen. so i dont have information regarding num of quantity fields. depending on the selection screen i may upload 10 quantitites or 20 quantites.......

what i need is i have to increase the number of columns of same type in an internal table .

Ex: my internal table has fields

1. Plant

2. Material

3.Version

4. quantity1

5 Quantity2

6 Quantity3

here i have 3 quantity fields , but i may upload 10 quantities. how to increase the number of quantity columns dynamically ???

Please let me know how to do this ?

Thanks in Advance

Regards,

Ajay