> For the complete documentation index, see [llms.txt](https://docs.mashmatrix.com/mashmatrix-sheet/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.mashmatrix.com/mashmatrix-sheet/functions_advanced/union_sheet/limitations.md).

# Limitations

A union sheet has the following limitations.

* You can select two or three objects for a single union sheet. The same object cannot be selected more than once.
* After a union sheet is created, you cannot add or remove the objects to unite, or change the order of the union.
* An ordinary sheet that has already been created cannot be converted to a union sheet.
* A union sheet cannot be created as a related sheet. However, you can link it to another sheet by specifying a reference value in a filter. For details, see "[Reference Value](/mashmatrix-sheet/functions_about_displaying_data/reference_value.md)".
* The "Object Type" column cannot be deleted. A group column that contains this column cannot be deleted either. It can be set to hidden.
* The "Object Type" of an existing record cannot be changed.
* Data columns and matrix columns cannot be used in a union sheet.
* In a column action, you cannot reference a value by specifying a field. You can use the method of referencing by specifying a column instead.
* The formula editor does not display the field tab for referencing the fields of an object directly.
* In "Show me" of the sheet setting, you can select only the options that can be specified in common for all the united objects.
* A filter group can be set only among columns that have the same composition of objects with fields assigned.
  * For example, in a sheet uniting accounts, contacts, and leads, a union column with fields assigned to account and lead and a union column with fields assigned to account and contact cannot be set in the same filter group.
* The "Object Type" column cannot be included in a filter group.