Creating Secondary Indexes
引用自:http://developer.mimer.com/documentation/html_92/Mimer_SQL_Mobile_DocSet/Defining_Database9.html
A secondary index is automatically used during searching when it improves the efficiency of the
search.
Secondary indexes are maintained by the system and are invisible to the user.
Any column(s) may be specified as a secondary index, except columns declared using a LOB data type.
Columns in the PRIMARY KEY, the columns of a FOREIGN KEY and columns defined as UNIQUE are
automatically indexed, (in the order in which they are defined in the key), and therefore creation
of an index on these columns will not improve performance.
Secondary index tables are purely for Mimer SQL's internal use - you create the index, and Mimer SQL
handles the rest.
If, for instance, you want to know which products were released on a specific date, Mimer SQL would
have to search successively through the entire ITEMS table to find all items that matched the date
you specified. If, however, you create a secondary index on release date, Mimer SQL would locate
that date directly in the secondary index, which would save time.
Secondary indexes can improve the efficiency of data retrieval; but introduces an overhead for write
operations (UPDATE, INSERT, DELETE). In general, you should create indexes only for columns that are
frequently searched.
Indexes cannot be created directly on columns in views. However, since searching in a view is
actually implemented as searching in the base table, an index on the base table will also be used in
view operations.
來自 “ ITPUB部落格 ” ,連結:http://blog.itpub.net/10599713/viewspace-983309/,如需轉載,請註明出處,否則將追究法律責任。
相關文章
- Creating Compressed Tables and IndexesIndex
- ORA-29857: domain indexes and/or secondary objects exist in the tablespaceAIIndexObject
- Secondary Indexes on Index-Organized Tables (231)IndexZed
- Miscellaneous Information about Creating Indexes on Partitioned TablesORMIndex
- Examples of Secondary IndexIndex
- Rebuild IndexesRebuildIndex
- ORACLE INDEXESOracleIndex
- Oracle - Tables/IndexesOracleIndex
- Reverse Key IndexesIndex
- ORACLE -> NULL & INDEXESOracleNullIndex
- Overview of Partitioned IndexesViewIndex
- Local Partitioned IndexesIndex
- Global Nonpartitioned IndexesIndex
- Extents in Indexes (19)Index
- 翻譯(九)——Clustered Indexes: Stairway to SQL Server Indexes Level 3IndexAISQLServer
- What is meant by Primary Index and Secondary IndexIndex
- skip_unusable_indexesIndex
- The Secrets of Oracle Bitmap IndexesOracleIndex
- Restrictions on Create Bitmap IndexesRESTIndex
- Global Range Partitioned IndexesIndex
- Global Hash Partitioned IndexesIndex
- Maintenance of Global Partitioned IndexesAINaNIndex
- Overview of Indexes (194)ViewIndex
- Indexes and Nulls (198)IndexNull
- Creating the Database (58)Database
- Sparse Indexes vs unique indexIndex
- SKIP_UNUSABLE_INDEXES InitializationIndex
- Choosing Composite IndexesIndex
- 建立Function-Based IndexesFunctionIndex
- How Indexes Grow and PctfreeIndex
- Bitmap Indexes and Nulls (224)IndexNull
- Partitioned Indexes on Composite PartitionsIndex
- 慎用 skip_unused_indexesIndex
- Delete indexes to free database.deleteIndexDatabase
- Unique and Nonunique Indexes (195)Index
- Composite Indexes (196)Index
- Indexes and Keys (197)Index
- Reverse Key Indexes (219)Index