Data Type QUAN

Hi Dear Expert,

I do not know too much about this data type. I have a requirement to extract data from two custom tables records to one alv table. So there are some different columns and some commom columns. Here there are two different fields that need to be shown using a shared alv table field. These two different field are: QUAN, 15 chars and decimal 3 without 'sing' flaged;    QUAN, 13 chars and decimal 3 with 'sing' flaged

So how do I set the filed type in the alv table???  Hope anyone could give me some hints. Thank you so much,

BR

Jay