http://help.sap.com/saphelp_nw70/helpdata/EN/e7/5f983c1a356858e10000000a114084/content.htm
For ex if you had designed a MP using the IC's and DSO's in which if all the fields are not in common with both the info provides used in the MP you will get the results in 2 rows and the values for the ones which are not in common will be displayed as # in the results.
This can be the case in Infosets as well.
to over come this we use "constant selection"
Check the below link which explain the constant selection with an example.
http://sapbi101.blogspot.com/2010/05/constant-selection-in-query-apples-and.html
Regards,
Venkatesh