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Function-Based Indexes. Traditionally, performing a function on an indexed column in the where clause of a query guaranteed an index would not be used. Oracle 8i introduced Function-Based Indexes to counter this problem.
A function-based index calculates the result of a function that involves one or more columns and stores that result in the index. The following shows the syntax of creating a function-based index: CREATEINDEX index_name ON table_name (expression);Code language:SQL (Structured Query Language)(sql)
10 sie 2017 · Indexes. They're one of the most powerful and misunderstood aspects of SQL performance. In this post we'll look at the purpose of an index, how to create and choose choose your index type. Then finish with a discussion of how to decide what to index and how to see if it's useful.
A function-based index computes the value of an expression that involves one or more columns and stores it in the index. The index expression can be an arithmetic expression or an expression that contains a SQL function, PL/SQL function, package function, or C callout.
Purpose. Use the CREATEINDEX statement to create an index on: One or more columns of a table, a partitioned table, an index-organized table, or a cluster. One or more scalar typed object attributes of a table or a cluster. A nested table storage table for indexing a nested table column.
This Oracle tutorial explains how to create, rename and drop indexes in Oracle with syntax and examples. An index is a performance-tuning method of allowing faster retrieval of records.
Function-Based Indexes and NULLs. ¶. By default Oracle does not store null rows in a (B-tree) index. You can add them with a simple trick: 1 CREATE INDEX index_name 2 ON tab_name ( nullable_col_name, 1 ); The ‘trick’ is of course nothing but a function-based index.
