Originally Posted by dmapr
For example, let's say I have a series (built-in column) John Doe and it has books 1-6 in it and another series (built-in) Jane Doe with books 1-3 & 5-7 in it. If I proceed to create a user-defined series column and place the value of Jane Doe in it for the John Doe then I would only want to see two series on the reader: John Doe (six books) and Jane Doe (seven books), with one book appearing in both series.
If I am understanding correctly, your proposal is that duplicate series names are the same series even if found in different columns, while duplicate words (tags or non-multiple text fields) do not have the same meaning if found in different columns.
I can imagine cases where the series assertion isn't true. For example, I might have a series field for publication order that uses the same names as the series column. One prime example would be MZ Bradley's Darkover books, where series order is very different from publication order. I would use the standard series order to indicate temporal ordering in the Darkover universe, while using a #pub_series column to indicate publication order. In this case I cannot merge the two columns.
I think that your proposal would be appropriate when one wants to say that a given book is in more than one series. I would create N series columns, where N is the maximum number of series a book can have, then put the series information in some column or another. I can see why you want this, but it does raise some interesting problems related to searching and sorting. In your example, if I ask for series:"Jane Doe", I would not see book 4. It would not be possible to sort the Jane Doe series into order. The disparity between what one sees on the reader and what one sees in Calibre concerns me, especially from a support standpoint. However, I could be fretting over nothing.