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Lesson 10 Creating a function-based index
Objective Create a function-based index.

Creating function-based Index in Oracle

Although the function-based index is new to Oracle, you create a function-based index in the same way that you create a standard index, as shown in the following MouseOver.
The first part of the CREATE INDEX statement is exactly like the standard form of the statement. After defining a name for the index and a table the index is associated with, you simply define the function on which the index will be based, rather than naming the columns that make up the index.
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1) Required keywords, 2)Unique index name, 3)Required keyword, 4)Unique table name, 5) The expression of the function on which the index is based
Function Based Index

When is function-based index used?

The Oracle cost-based optimizer will use a function-based index if it can be used as part of the execution path. Just as with the materialized view, discussed in the previous module, the use of a function-based index is transparent to the user. However, to guarantee that the function-based index will be used, you should also include a condition that guarantees that the result of the function in the query will not return a NULL value.
For instance, if you created a function-based index based on applying the UPPER() function to the NAME column, the following SQL statement would use the function-based index.


You can use more than just a simple function like UPPER() in a function-based index. A function-based index can use a more complex arithmetic calculation or even a PL/SQL function that you define yourself. You cannot use an aggregate function, such as SUM(), for a function-based index.
Because the function-based index is recognized only by the cost-based optimizer, you must gather statistics on the index with the ANALYZE command before it will be used by the optimizer. The next lesson is the module wrap-up.

Create Function Based - Exercise

Click the Exercise link below to practice creating an index-organized table.
Create Function Based - Exercise

Function-Based Indexes

You can create indexes on functions and expressions that involve one or more columns in the table being indexed. A function-based index computes the value of a function or expression involving one or more columns and stores it in the index. A function-based index can be either a B-tree or a bitmap index. The function used for building the index can be an arithmetic expression or an expression that contains a SQL function, user-defined PL/SQL function, package function, or C callout. For example, a function could add the values in two columns.

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