Null value in source field causes incorrect & unexpected results on rare occasions

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Hi,

I have been trying to track down this problem for weeks, and believe I finally 
have a way of replicating this issue for demonstration.

I have been experiencing on the vary rare occasion results from TxQuery that 
have not grouped / combined matching records together, where the result gives a 
separate record for every record in the source dataset.

It appears as though the problem has to do with null values in one of the 
fields. This problem does not happen with all result sets, and strangely enough 
- if I add an additional record to the existing result set, the problem 
dissapears (hence it being very difficult to replicate).

However, I have now been able to create a demo application that will show both 
the problem, as well as what the expected result should be (attached).

Steps to replicate:

1) Extract the attached demo project, along with the table (xquery.dbf) to a 
destination

2) Open the project, and change the path of the TicketQAQ.DatabaseName to the 
location of the extracted files. 

3) Run the project. If you click on the RUN USING BDE button, you will see a 
result set with many records - where it does not group as expected.

4) Click on the Remove Contract from XQUERY button, and then the RUN USING BDE 
again - and the resultset will be only 3 records - as I expect it to be.

This problem occurs not only with the BDE, but also with another database 
(DBISAM). It took me some time to be able to replicate the issue using the BDE 
to submit an example project.

This problem is currently plaguing my software, so I'm excited to finally 
hopefully finding a solution. Any help will be greatly appreciated!

I am using Delphi 2007 just incase this is isolated to pre-XE software.

Best Regards

Adam.

Original issue reported on code.google.com by wsdah...@gmail.com on 18 Jun 2013 at 11:45

Attachments:

• xqueryproblem.zip