15.10 - Optimized Method of Maintaining a Join Index During DELETE Operations - Teradata Database

Optimizations have been made for update statements that allow the affected join index rows to be located via direct access. For example, if a DELETE request specifies a search condition on the primary or secondary of a join index, the affected join index rows are not reproduced. Instead, the join index may be directly searched for the qualifying rows and modified accordingly.

To use this optimized method (that is, the direct update approach), the following conditions must be present.

A primary or secondary access path to the join index.

If join_index_column_2 is defined, no modifications to join_index_column_1 columns.

No modifications to the join condition columns appearing in the join index definition.

No modifications to the primary index columns of the join index.

The following is an example of an optimized method for maintaining join index during a DELETE request:

   EXPLAIN DELETE FROM lineitem

           WHERE l_orderkey=10;

    *** Help information returned. 11 rows. 

    *** Total elapsed time was 2 seconds.

Explanation

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  1) First, we execute the following steps in parallel.

       1) We do a single-AMP DELETE from join index table

          df2.OrderJoinLine by way of the primary index

          "df2.OrderJoinLine.l_orderkey = 10" with a residual

          condition of ("df2.OrderJoinLine.l_orderkey = 10").

       2) We do a single-AMP DELETE from df2.lineitem by way of the

          primary index "df2.lineitem.l_orderkey = 10" with no

          residual conditions.

  2) Finally, we send out an END TRANSACTION step to all AMPs involved

     in processing the request.

  -> No rows are returned to the user as the result of statement 1.