Grouping Using Yii Ireport Extension

I am using iReport extension in yii to display a report. I want to group the result based on a field.For example the result set has three fields voucherno,itemname and suppliername. So the same voucher number will have many items. I want to group it using voucherno and display the items of each voucherno using iReport.

I am using PostgreSQL as the database. I was able to connect iReport designer with postgresql and was able to display the fields. I followed the tutorial here If I run the preview in iReport designer then it is showing correctly. But in yii iReport extension only the first group head is getting displayed. For the rest groups the detail part is displayed. Please help.