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This article introduces the relevant knowledge of "what are the types and characteristics of database index". In the operation of actual cases, many people will encounter such a dilemma. Next, let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

To effectively optimize the VPS performance and improve the running speed of the VPS server, in addition to reasonably configuring the WEB server, what is more is that we need to be able to optimize the website program and the website database. The most basic optimization measure for the optimization of the website database is to establish the database index. Here, what is the database index? What are the types and characteristics?

⑴, what is a database index?

A database index is a structure that sorts the values of one or more columns in a database table, using the index to quickly access specific information in the database table. In a database, the meaning of an index is not much different from the word "index" in the daily sense (think about looking up a dictionary when you were a child). It is a database object used to improve the speed of database table data access.

① in some cases, indexes can also be used to avoid sorting operations

② for nonclustered indexes, some queries may not even access the data page

③ indexes can avoid full table scans. Most queries can scan only a small number of index pages and data pages instead of traversing all data pages

④ clustered indexes prevent data inserts from focusing on the last data page of the table.

Of course, although the database index can effectively improve the query speed of database data, it will also lead to a decline in the performance of the database system to update data, because most data updates need to update the index at the same time.

⑵, type of database index:

The database index is like the catalog in front of a book, which can speed up the query of the database. Depending on the functionality of the database, three indexes can be created in the database designer: unique index, primary key index, and clustered index. Although a unique index helps to locate information, it is recommended that you use a primary key or unique index instead for best performance results.

① clustered index, where table data is stored in the order of the index. For clustered indexes, the leaf node stores real rows of data, and there are no separate data pages

② nonclustered index, the order in which table data is stored is independent of the index order. For nonclustered indexes, the leaf node contains the index field value and a logical pointer to the data row of the data page, which is adjacent to the data page, and the number of rows is the same as the amount of data in the data table row.

Only one clustered index can be created on a table, because the physical order of real data can only be one. If a table does not have a clustered index, it is called a Heap. There is no specific order for the data rows in such a table, and all new rows will be added at the end of the table.

⑶, the basic characteristics of database index:

The purpose of indexing is to speed up the lookup or sorting of records in a table. There is a price to pay for setting an index for a table: one is to increase the storage space of the database, and the other is to spend more time inserting and modifying data (because the index has to change with it). A database index is a catalog of values in certain fields in order to improve the efficiency of table search. The database index is built on top of some columns in the database table. When creating a database index, you should consider which columns can and cannot be indexed. In general, indexes should be created on these columns.

Through the understanding of the knowledge and basic characteristics of the database index, it is not difficult to find that the establishment and use of the database index plays an extremely favorable role in providing the overall performance of the database system, and can effectively speed up the reading speed of the database. But at the same time, there are some drawbacks. The creation and maintenance of database index and storage will not only consume a lot of time and energy. At the same time, it will also consume resources such as the hard disk space of the VPS server, so for the maintenance of large databases, we also need to be careful to use database indexes.

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