Historians don't really store data directly in database tables, but provide an SQL type interface for querying data, as well as an API or SDK for developing additional applications (you see these used with the UDS and PCO connectors). Historians use a proprietary compressed file format for the actual data storage, and in some cases the tag configuration is stored in relational tables, but the data is retrieved when you query it. In the case of your question concerning History mode, it is actually interpolated values from the raw archived values.
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