Let's talk about IOT and mappingtable.

As a trainer for many years, when students have completed Chapter 10th or 11g related chapters of 1Z0-043, they often don't know What IOT and mappingtable are doing. Let me say a few words about these two things: 1) when you create an IOT table

As a trainer for many years, when students have completed Chapter 10th or 11g related chapters of 1Z0-043, they often don't know What IOT and mappingtable are doing. Let me say a few words about these two things: 1) when you create an IOT table

As a trainer for many years, when students have completed Chapter 10th or 11g related chapters of 1Z0-043, they often don't know What IOT and mappingtable are doing. Let me say a few words about these two things:

1) when you create an IOT table and want to create a bitmap index for one of the above columns (of course, other columns with non-primary keys) (note that it is not a common B-tree ),, you must create a mappingtable. ---- Required. Have you noticed the error message when mappingtable is not found?
2) Check user_objects and find the object_id of IOT. Use this object_id:

Select * from dba_tables where table_name like '% object_id %' just found ';

Find the table with the mapping word, which is the mappingtable.

3) Note that Mappingtable is a heaptable used to store the logic rowid of IOT. Each row of the Mappingtable stores the logicalrowid recorded in the corresponding IOT table. Therefore, this mappingtable maintains the row location relationship of the IOT table.

4) Why?
Because the rowid stored in the bitmap index entries must use physicalrowid, IOT cannot provide stable physicalrowid, so bitmapindex can only record the physicalrowid of the mappingtable. The execution plan accessed through the bitmap index is probably to first access the mappingtable Based on the mappingtablephysicalrowid recorded in the bitmapindex, and then access the IOT table through the logicalrowid in the mappingtable.

A metaphor: The curve saves the nation.

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