I have written before about databases that take selection criteria from Crystal and then use the wrong index so that valid records are missing from the results. The solution is to write the criteria so those rules don’t make it into the SQL WHERE clause. Crystal can then apply that criteria locally so it is done correctly.
But today I ran into a similar problem that didn’t have a simple solution. I was creating a report to read Elliot data. Elliot is what used to be called Macola Accounting. We were connecting to a Pervasive SQL DB using an ODBC connection. We were trying to link the Item file to a second instance of the Item file to get a list of components for manufactured items. What we found is that when we joined the component ID from instance one to the part ID in instance two, the results would not return a single match between the two tables.
Looking at the tables separately showed the matching data was there. And when I tried to filter to a single PartID the results would not find that ID. This is when I realized that we had an index problem like the one I described above.
So I looked at the index tabs in the Database Expert and noticed that this table had two red index tabs, meaning there were two fields in the primary index. The tabs were on Item Number and Sequence number. We were linking from a table where there was a component item number but there was not a component sequence number. It appears that Pervasive SQL defaults to using the primary index for ODBC joins, even if the fields you are using for the join don’t completely match the fields in the index. So the link will fail every time. I even unchecked the option “use indexes or server for speed” to see if that would help, but it didn’t have any affect.
We were lucky that the table we were using had an equivalent view. We linked this view to itself and we were finally able to find matching records. I assume this worked because this view, like most views, are not indexed.