Whereas with branch merging, you can add more records to the 2 lists of matching records, in File merge the lists are given and are fixed. One list (in the centre of the Merge/Compare dialog) consists of all the records in the current file. The other list (on the right) consists of all the records in the file that you wish to merge or compare with the current file.
If you unmatch records as part of a branch merge, the records will cease to be listed in the Merge/Compare dialog. If you unmatch records as part of a file merge, the records will continue to be listed but will not display as matched (i.e. lined up in the same row). An unmatched record will have a blank row next to it in the neighbouring list.
You cannot discard records as part of a branch or basic record merge. But in a file merge you can. The meaning of the discard action depends on whether the selected record belongs to the current file or to the one that you wish to merge or compare with the current file. If the record belongs to the current file, discarding a record means deleting it from the current file. If, on the other hand, the record belongs to the file being merged/compared with the current file, discarding that record means simply that the record will not be added to the current file as part of the merge.
Bear in mind that, as with matching and unmatching, no changes to the current file happen when you discard a record. ‘Discarding‘ a record simply indicates what you want to happen when the button is pressed.
‘Retaining’ a record simply undoes the effect of ‘Discarding’ it.