There is a way to create openings of any forms and make holes using it.
1. Make a level with elevation equal to floor thickness
2. Draw needed shape with room tool. Off showing area and ceiling for the room.
3. Make wall (and rooms) fully transparent on 3D by Modify 3D view/Walls transparency 100%
4. Take any existing transparent opening or just any piece of furniture, make it microbe size, put near of your room and "copy as new furniture" (it is plugin) room and opening together. The reason you need small piece also - button "copy as new furniture" doesn't work with rooms only, you need some furniture also. You may try to use ОBJ export/import instead of this plugin.
5. Paste your room, now you have transparent оbject. Then you need to rotate it to 90* several times. To understand needed angles you may train on half-transparent objects.
6. Export transparent object to ОBJ, and import as a furniture door/window. Now you have transparent opening
7. Make walls nontransparent back, draw wall with dimension of table top; and put new opening to the wall - then you have hole.
8. Copy the wall with hole "as furniture" or use OBJ Export/import; rotate it, add texture - now you have table top with hole
