[development] adding a filter to views

[Lluís]

I have just created a module to allow user to insert a field in a view
which is the add of two other numeric fields in the view; so the
resulting SQL is like:
SELECT a,b, (a+b) c FROM table

My approach is different from views_calc because it should work on
grouped fields so:
SELECT d, sum(a), sum(b), (sum(a)+sum(b)) FROM table GROUP BY d

Now I need to add a filter and I don't know really where to start; I
suppose I should start from views_handler_filter_numeric but I don't
know anything else.

Any hint is welcome; and if anybody is interested in this module I can send it.

Thanks

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