Thank you for writing.
One scenario to achieve this is to fill a DataSet with all the tables from the access database and use the data set to bind the grid and drop down. When the user is done editing you can commit the changes back into the database. The provider you use to read/write the data from/to the database is up to you. Once you have the DataSet set up, you can bind the drop down list to the tables collection of the data set. On the SelectedIndexChanged event of the drop down you should bind the grid to a different table from the data set. Please find attached a sample project where I create a DataSet with two tables and mimic the scenario you have described.
I hope you will find this useful. If you have further questions, I would be glad to help.
All the best,
the Telerik team
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