Subject Historic tables design
Author Aldo Caruso

it is common in some business rules that a table has a companion
table of historic records. The historic table has the same structure
than the active records table, but is less accessed than the active
table. On the other hand, the historic table grows steadly, ending up
with far more records than the active one ( records deleted from the
active table go to the historic one ).

My question is the following: should both tables be merged into a
single table, with an additional field marking historic records ? Will
the queries on this table be slower than having them separated ?

I know that an index taking into account that additional field
would speed up the queries but, on the other hand, such an index would
be a very poorly selective one, because the additional field would only
have two values ( 0 and 1 ) like any boolean field.

Thanks for any advice.