Example: Increase Order occurs before Reduce Discount - Advanced SQL Engine - Teradata Database

Assume the individual transactions have the following characteristics:

• Begin Time is the value of TEMPORAL_DATE for the example transactions. This time is used both to qualify rows for participation in the transaction, and to timestamp the modified rows.
• Modification Time is the time when the modification is made by the transaction.
• End Time is when the transaction is committed and completed.

Notice that Increase Order ends before Reduce Discount begins.

The following shows the states of the Orders and Parts tables after transactions have completed.

Orders table state after the Increase Order transaction:

In the original state of the tables, the P1 rows qualified for the CURRENT transaction because their valid times overlapped current time, value of TEMPORAL_DATE at the time when the transaction started, shown as Begin Time in the table of transaction characteristics. The period (2008-01-01, 2011-01-01) overlaps 2009-01-02.

Additionally, the P1 row in the Orders table was modified, because the P1 row in the Parts table fulfilled the transaction WHERE test (discount >= 10).

The modification of the P1 row in the Orders table leaves a history row showing the state of the row prior to the modification. Notice the end time of the first row and the beginning time of the second row have both been timestamped with TEMPORAL_DATE at the time of the modification.

Parts Table state after the Reduce Discount transaction:

The P1 row was not changed, because the current time at the time of the Reduce Discount transaction was 2009-01-09. Using this current time, only the second row in the Orders table qualifies for the transaction, however that row fails the WHERE test (quantity < 100), due to the changes made by the preceding Increase Order transaction.