Database Reference
In-Depth Information
• When the Explain Plan button is clicked, the screen will be divided into two halves, as
shown in the illustration. The upper half of the screen will show the SQL statement
and how it is executed in the Oracle Database. The lower half of the screen will give
you the execution plan.
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• The execution plan gives you the details on the processing of the selected SQL state-
ments such as estimated costs and estimated rows.
• The estimated cost is the number based on the access optimization by the cost-based
optimizer. Estimated costs are proportional to the number of blocks necessary to read
to fulfill the request. Higher costs could indicate a problem. The estimated rows indic-
ate how many rows might be found as a result of the select statement.
• In the same screen clicking the individual tables and indexes (
Figure 22-3
) will
provide detailed information about the last analysis and the collected statistics for the
object.
