How to group results by multiple fields? I have values in database like: 

x submits file 1

x submits file 2

y submits file 1

y submits file 3

x submits file 1(again)

I had my output with aggregation settings as group results together as

x submits file 1

x submits file 2

y submits file 1

y submits file 3

it just grouped file 1 submissions of x 

i want it to be :

x submits file 1,2

y submits file 1,3

Can anyone please help?
In D7 - you can achieve your grouping structure in Views with the help of the Views Merge Rows module.

You'd use the option "Use values of this field as a filter" for the field that produces x &amp; y. And for the file name field you'd use the option "Merge unique values of this field".