If I want to perform **Union** operation between Excel and CSV files by ignoring the missing files, I would enable the option **Ignore route errors** in the Delimited Datasource.
By enabling this option, I was able to avoid the errors from CSV files and retrieve the results of union view successfully.
Additionally, if there is a data level error like the CSV file that do not have the expected structure, then you could make use of the **Ignore matching errors**. If this is enabled, the Server will ignore the lines of this data file that do not have the expected structure.
You can have a look at the [**Delimited File Sources**](https://community.denodo.com/docs/html/browse/7.0/vdp/administration/creating_data_sources_and_base_views/delimited_file_sources/delimited_file_sources) for more information.
Hope this helps!