The main table would still hold the entire current record. Even if the history table contains the current record, you don't want to get it from there because of the additional overhead. That table could have dozens or hundreds (or thousands or ...?) copies of the rows, one for each change. When you need the currently version of a row, which is presumably the most common read, it's vastly less overhead to read it from a table that contains only the current version of rows instead of the entire history of all rows.