Direct row access (PRIMARY_ACCESSTYPE='D')
If an application selects a row from a table that contains a ROWID column, the row ID value implicitly contains the location of the row. If you use that row ID value in the search condition of subsequent SELECT, DELETE, or UPDATE operations, DB2® might be able to use direct row access navigate directly to the row.
To use direct row access, you first select the values of a row into host variables. The value that is selected from the ROWID column contains the location of that row. Later, when you perform queries that access that row, you include the row ID value in the search condition. If DB2 determines that it can use direct row access, it uses the row ID value to navigate directly to the row.
If an application selects RID built-in function from a table, the result contains the location of the row. If you use the RID built-in function in the search condition of subsequent SELECT, DELETE, or UPDATE statements, DB2 might be able to choose direct row access to navigate directly to the row. For a query to qualify for direct row access, the search condition must be a Boolean term stage 1 predicate that fits one of these descriptions: If DB2 cannot locate the row through direct row access, it does not switch to another access method and just returns no row found. The EXPLAIN output in the PLAN_TABLE is changed if DB2 chooses the direct row access when the above conditions are satisfied, with the RID built-in function used as a search condition.
