- The valid-time period should always be explicitly specified when adding rows to tables that have a valid-time column.
- An explicit time period should always be specified when making DML modifications to tables that have a valid-time column. This specifies the period of applicability (PA) of the change, which may not exactly match the PV of any row. If the PA of a modification does not match the PV of a row, Teradata Database determines how to make the change by the relationship between the PA and PV. If the PA and PV overlaps, the modification involves adding new rows to the table to account for the period before and after the change.
Although the PA and PV can be explicitly specified for operations on tables with valid-time columns, Teradata Database will use default values if these periods are not specified. For valid-time tables, the current time at the time of a row insertion or modification is timestamped as the value of the built-in function TEMPORAL_TIMESTAMP, or TEMPORAL_DATE if the valid-time column has a DATE type.
The value of TEMPORAL_TIMESTAMP or TEMPORAL_DATE for a transaction is the time or date when the first non-locking reference is made to a temporal table, or when the built-in function is first accessed during the transaction.
For more information on TEMPORAL_TIMESTAMP built-in function, see Teradata Vantage™ - SQL Functions, Expressions, and Predicates, B035-1145.