How to show customer attirbutes of work item in birt report?

I defined some customer attirbutes for work item
our client request show work item list with all atribute in a list report,and do some group account for some customer attirbutes.
The query result can show ,but client is not satisfied with it.
Then I try BIRT,
and can show the attributes which are defined by RTC which are store in RTC as a table column
but the customer attirbutes are not store in RTC as a table column,
I found they are stored by two column,one is string_key,the other is string_val,so a work item have serveral item in WORKITEMS_SNAPSHOT/LIVE_WORKITEM_CNT table.
Which means the customer attirbutes cannot be select and list.
I search related topics in jazz fortums,found that can define a WORKITEM QUERY REPORT,which use the data in WORKITEM_QUERY_RESULTS table.
I try ,but found the table is empty.
Is there anyone have the same problem?
can someone help to resolve it ?
thank you !!!