How to combine different editions of the same book in Calibre?

My suggestion is to select the two book records of different format, and do as follows,

1. Edit metadata
2. Merge book records,
3. Merge only format into first selected book - delete others

Or for short cut, select the two book records with different format, "ALT SHIFT M"

BTW, I've read in previous version Calibre used this option for merging them,

Turn on the autosort/automerge option located at Preferences|Add/Save|"If books with similar author and title found ...."

It will cause Calibre to identify the second book by author and title, determine if there is another matching book with that author/title and then add the new format to the existing matching record.

My version is calibre 0.8.38

I have been looking for the answer to that also. From what I have found you have to add them as two separate books. Make the title contain the edition info.

If you add them with same metadata the last one will overwrite the previous one.