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You can restore any dropped table, as long as it is still listed in the Recycle Bin, by using the FLASHBACK TABLE table_name TO BEFORE DROP command (at which point Oracle will also remove it from the Recycle Bin). The following example would restore the previously dropped persons table. SQL> FLASHBACK TABLE persons TO BEFORE DROP; Flashback complete. SQL> Alternatively, you can use the system-generated table name: SQL> FLASHBACK TABLE "BIN$xTMPjHZ6SG+1xnDIaR9E+g==$0" TO BEFORE DROP; Flashback complete. SQL> As part of the Flashback operation, you may want to rename the previously dropped table, as follows (you can use either the system-generated or original table name): SQL> FLASHBACK TABLE "BIN$xTMPjHZ6SG+1xnDIaR9E+g==$0" TO BEFORE DROP RENAME TO NEW_PERSONS; This is particularly useful when you ve already created a new table with the same name as the dropped table. If you drop a table and then create a new one of the same name, it s possible (if you then drop that new table) that the Recycle Bin will contain several versions of the dropped table, each with a unique system-generated table name. If you then issue a FLASHBACK TABLE . . . TO BEFORE DROP command using the original table name, Oracle will simply recover the latest version of the table. If you want to return to an older version you can then simply reissue the same command until you recover the required version. Alternatively, you can provide the specific system-generated name of the table you want to recover.

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The script consists of a loop that repeatedly computes trajectory values based on the current inputs and then updates the input values based on the user s keystrokes. The following code section is where the calculations are performed for the values we seek. Every iteration of the loop recalculates the projectile s distance, height, and duration.1

Every time you need to access a view, Oracle must execute the query that defines the view in question and get you the results. This process of populating the view is called view resolution, and it must be done afresh each time a user refers to the view. If you re dealing with views with multiple JOIN and GROUP BY clauses, this process of view resolution could take a very long time. If you need to access a view frequently, it is very inefficient to have to constantly resolve the view each time. Oracle s materialized views offer a way out of this predicament. You can think of materialized views as specialized views that have a physical representation, unlike normal views. They occupy space and need storage just like your regular tables. You can even partition materialized views and create indexes on them if necessary.

A view is always computed on the fly, and its data isn t stored separately from the tables on which it s defined. Thus, queries using views, by definition, guarantee that up-to-the-minute data will be returned. Any change in the source tables on which the view is defined will be reflected by the view instantaneously. Materialized views, on the other hand, are static objects that derive their data from the underlying base tables. If you refresh your materialized views infrequently, the data in them may be at odds with the data in the underlying tables.

Traditionally, data warehousing and other similar large databases have needed summary tables or aggregate tables to perform their work. Defining these summary tables and constantly maintaining them was a complex task. Any time you added data to the underlying detail table, you had to manually update all the summary tables and their indexes. Oracle s materialized views offer a way to simplify summary management in large databases. Materialized views in these environments are also called summaries because they store summarized data. You can use tables, views, or other materialized views as the source for a materialized view. The source tables are called master tables, and it s common to refer to the master tables as detail tables in a data warehousing environment. When you create a new materialized view, Oracle will automatically create an internal table to hold the data of this materialized view. Thus, a materialized view will take up physical space in your database, whereas a regular view doesn t, since a view is only the output of a SQL query. Oracle will also automatically create at least one index on the materialized view and may create a view as well. You can do the following with a materialized view: Create indexes on a materialized view Create a materialized view on partitioned tables Partition a materialized view

You can use an index to access a materialized view directly, as you would a table. Similarly, you can also Tip access a materialized view directly in an INSERT, UPDATE, or DELETE statement. However, Oracle recommends that you not do so, and that you let the Oracle cost-based optimizer (CBO) make the decision about whether to rewrite your normal queries to take advantage of a materialized view. If the execution plan using the materialized view has a lower cost of accessing it compared to accessing the tables directly, Oracle will automatically do so.

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