Cartographica uses ODBC to connect to databases. Many people make use of the fine ODBC connectors from Actual Techologies, which are commercial-grade, professionally-supported ODBC connectors for the Macintosh that will connect to any number of open source databases, Oracle, or Microsoft Access format files.
However, if you are using the demo versions of their connectors, they only support loading in 3 records at a time. So, if you are using the demo version, or if you have recently changed your configuration on your Macintosh and might have lost your key preferences of Actual Technologies' software, Cartographica will see every database from them as containing only 3 records.
The solution is to get the full version of their connectors once you have been able to load the test records.
There are alternative open-source ODBC connectors available for some databases as well.