Let me know about drill by please my dear friends....

Drill through  is process of converting summarized data into
detailed data.......we can say like this simplyyy

  Drill Through to Cognos Query

To set up drill through from PowerPlay Web to a Cognos Query
report, you must perform the following tasks:

    * In Cognos Query, save the query you want to drill
through to as an .iqd file.
    * In Transformer, specify the drill-through targets
(.iqd files) for your measures or PowerCubes. You must then
update all affected cubes .
    * In PowerPlay Enterprise - Server Administration,
enable drill through and specify the required URL to start
Cognos Query. 

Notes

    * When a drill through is executed, it passes the
current dimension line settings as filter parameters. If the
.iqd file cannot apply these filters, due to incorrect
column labeling, the drill through may return unexpected
results.
    * For a drill-through request to execute properly, a
copy of the .iqd file must be replicated on the target
Cognos Query server. The path must be the same relative to
the folder in which Cognos Query is installed on the target
server.
    * When performing a drill through, only the current
dimension line settings are passed as filter parameters to
the drill-through target. Unlike PowerPlay client, where the
active cell is also passed with the dimension line setting,
PowerPlay Web does not identify an active cell. 


Design Queries as Drill-through Targets

The design criteria for a drill-through query are different
from a cube creation query in the following ways:

    * Drill-through queries typically include many
non-additive text properties that you would not include in a
Transformer source query, such as Addresses and Phone
Numbers. These columns are the objective of drilling through.
    * Drill-through queries should include links to other
entities for further exploration. There is no reason to
include links in .iqd files that you intend to use only for
cube creation (not as drill-through queries).
    * Queries used as drill-through targets must be saved in
a folder that all the drill-through users have access to.
    * Queries used as drill-through targets should contain
the attributes used to define levels in the cube. Cognos
Query can only filter on attributes included in the query. 


Save a Drill-through Target in Cognos Query

PowerPlay Web requires an .iqd file to drill through to
Cognos Query. To create the .iqd file, you must enable drill
through for the report in Cognos Query and re-publish the
report to Upfront. The .iqd file will be created.
Steps

   1. In your Web browser, open or create a Cognos Query
report to which you want to drill through.
   2. On the Cognos Query toolbar, click the Design button.
   3. On the Advanced tab, click Properties.
   4. Select the Enable Drill-Through Access check box.
   5. Click the Run Query button.
   6. On the Cognos Query toolbar, click the Save As button.
   7. Follow the steps in the NewsItem wizard, and click Finish.

      The Cognos Query report reappears in your Web browser
and the .iqd file is created on the computer where the
Cognos Query server is installed. 

      Note: After you create the .iqd file, you must use
Transformer to specify the drill-through targets (.iqd
files) for your measures or PowerCubes and update the cubes
that you want to drill from . 

Notes

    * Ensure that you use Cognos Query to create your .iqd
files for drill through from PowerPlay Web to Cognos Query.
Do not use .iqd files from Impromptu. 


Enable Drill Through to Cognos Query

After you set up your .iqd drill-through targets and update
your cubes, you can enable drill through in PowerPlay
Enterprise - Server Administration.
Steps

   1. In PowerPlay Enterprise - Server Administration, click
a cube, report, or folder.
   2. From the Edit menu, click Properties, and then click
the Settings tab.
   3. In the Cognos Query box, click Enable.
   4. In the Cognos Query Server box, select the URL for the
Cognos Query gateway, such as
http://servername/cognos/cgi-bin/cqcgi.exe
   5. To test that the drill through works, click Open with
Browser on the Tools menu. Then drill through by clicking
Drill Through and selecting the target report.

Drill through to Cognos Query is now enabled.

Go through this link 
http://apsdwh.vlaanderen.be/cognos/help/html/ppwb/nl/pes_drill_through5.html