If a public synonym for a function, package, or type is used in column_expression, and later an actual object with the same name is created in the table owner's schema, then Oracle Database disables the function-based index. For example, this statement is guaranteed to use the index: Without the WHERE clause, Oracle Database may perform a full table scan. If you omit this clause, then Oracle Database sets PCTFREE to 10 and INITRANS to 2. No action is required by you when you issue the CREATE TABLE or ALTER TABLE statement to create the index, but you can optionally specify a USING INDEX clause to exercise control over its creation. To create an index in your own schema, one of the following conditions must be true: The table or cluster to be indexed must be in your own schema. Restriction on COMPUTE STATISTICS Clause You cannot specify this clause for a domain index. For nonunique indexes, the valid range of prefix length values is from 1 to the number of key columns. See CREATE TABLESPACE for examples that create tablespaces tbs_2, tbs_3, and tbs_4. Indexes can be unique or non-unique. REVERSE  Specify REVERSE to store the bytes of the index block in reverse order, excluding the rowid. table_name Function-based unique indexes can be useful in defining a conditional unique constraint on a column or combination of columns. Oracle 11g allows indexes to be marked as invisible. You can set the storage options for the indexes associated with UNIQUE and PRIMARY KEY constraints using the USING INDEX clause. However, a star schema is not a requirement for creating a join index. You cannot specify DESC for a reverse index. The default prefix length is the number of key columns. Oracle indexes - create, rebuild, select, drop. A bitmap index can have a maximum of 30 columns. If the name conflicts with an existing index subpartition name, then the database uses the form SYS_SUBPn. Creating an index using key compression enables you to eliminate repeated occurrences of key column prefix values. The SQL statement below creates an index named "idx_lastname" on the "LastName" column in the "Persons" table: CREATE INDEX idx_lastname. However, it is advisable that any index that exists for query performance, including unique indexes, be created explicitly. This section contains the following topics: Creating an Index Associated with a Constraint, Collecting Incidental Statistics when Creating an Index. Use the CREATE UNIQUE INDEX statement to create a unique index. Additionally, to use a function-based index: The table must be analyzed after the index is created. This setting also determines whether subsequent Direct Loader (SQL*Loader) and direct-path INSERT operations against the index are logged or not logged. Invisible Indexes in Oracle Database 11g Release 1. En general mejoran el rendimiento las SELECT y empeoran (minimamente) el rendimiento de los INSERT y los DELETE . SQL> Partitioned Tables. You must have the CREATE ANY INDEX system privilege. Also, sometimes an index needs to be rebuilt to help with performance. If the definition of a function-based index generates internal conversion to character data, then use caution when changing NLS parameter settings. Function-based indexes, which are based on expressions. Restriction on Key Compression You cannot specify COMPRESS for a bitmap index. For a nonunique secondary index on an index-organized table, the number of index key columns plus the number of primary key columns that are included in the logical rowid in the index-organized table cannot exceed 32. You can create an index on a scalar object attribute column or on the system-defined NESTED_TABLE_ID column of the nested table storage table. The column_expression can be any form of expression except a scalar subquery expression. When you specify column_expression, you create a function-based index. Your email address is your username. Scripting on this page enhances content navigation, but does not change the content in any way. You can specify NOSORT to indicate to the database that the rows are already stored in the database in ascending order, so that Oracle Database does not have to sort the rows when creating the index. Non-unique indexes do not impose this restriction on the column values. Create indexes after inserting table data and index on the correct tables / columns, that are most used in queries. For complete information on this clause, please refer to parallel_clause in the documentation on CREATE TABLE. The index contains the index key and the logical rowid of the index-organized table. However, in descending unique indexes, multiple NULL values are treated as duplicate values and therefore are not permitted. Note: For complete details on index create performance, see my book "Oracle Tuning: The Definitive Reference".When using the create index syntax to build an Oracle index, there are many options that can dramatically improve the speed of the creation, the space used by the index, and the height of the resulting index. If you do not specify storage options (such as INITIAL and NEXT) for an index, the default storage options of the default or specified tablespace are automatically used. New indexes can be automatically created as compressed, or the existing indexes can be rebuilt compressed. It seems like this is a common approach to slow queries. (local_partitioned_index ::=, index_attributes::=), (global_partitioned_index ::=, local_partitioned_index ::=, index_attributes::=, domain_index_clause ::=), (physical_attributes_clause ::=, logging_clause::=, key_compression=, parallel_clause::=), (index_partitioning_clause::=, individual_hash_partitions::=, hash_partitions_by_quantity::=), (on_range_partitioned_table ::=, on_list_partitioned_table::=, on_hash_partitioned_table ::=, on_comp_partitioned_table ::=), (physical_attributes_clause ::=, logging_clause::=, (segment_attributes_clause::=, index_subpartition_clause::=). If you also do not specify tablespace storage for index, then the database stores the subpartition in the same tablespace as the corresponding table subpartition. Name resolution of the function is based on the schema of the index creator. If you omit partition, then Oracle Database generates a name with the form SYS_Pn. Specify the schema to contain the index. 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