In a valid-time table, a history row is a row that is no longer valid: a row with a valid-time period that ends before the current time. A row with a valid-time value of NULL is not considered a history row.
In a transaction-time table, a row that is closed is also considered to be a history row, regardless of the valid-time period. See Closed Row.
In a bitemporal table, a history row is a row with a valid-time period that ends before the current time, or a row that is closed in transaction time, or a row that has both of these conditions. A row with a valid-time value of NULL is not considered a history row.