Every row in a temporal table is associated with at least one time dimension by having a corresponding time period. Special temporal SQL qualifiers for SELECT statements (AS OF, BETWEEN ... AND, FROM TO, and CONTAINED IN) allow you to query the data based on these time dimensions. For example:
- For system-time tables, you can query the data that is currently active, as with any table, but you can also query inactive rows to determine when in the past these rows were modified or deleted. Although these rows no longer participate in most SQL operations, they remain in the table, and can be queried using special temporal SQL.
- For valid-time tables, you use temporal SQL to see only rows that are currently valid, or rows that are, were, or will be valid during or within a period of time you specify. You can choose to limit queries to history rows that were valid at earlier times but are not valid now, or future rows that will not become valid until a time in the future.