What Is Automatic Indexing?

In a relational database, an index is a storage structure that sorts the values of one or more columns in a database table separately and physically. It is a collection of one or more column values in a table and the corresponding pointing table. List of logical pointers in a data page that physically identifies these values. The index is equivalent to the catalog of a book, and you can quickly find the content you need based on the page numbers in the catalog.

index

(Database term)

In a relational database, an index is a storage structure that sorts the values of one or more columns in a database table separately and physically. It is a collection of one or more column values in a table and the corresponding pointing table. In a data page that physically identifies these values

Formerly known as general inspection, preparation for inspection or lead. The basic unit of composition is the index entry. The entry generally includes three items: index words, descriptions or notes, and sources. All indexed items are arranged in an orderly manner. Its essential feature is that it only reveals the source of the content or documentation clues, and does not directly provide the facts and information itself. The main function is to provide clues for people to obtain accurate and rapid documentation. Common indexes include newspapers and periodicals materials index, corpus index, term index, sentence index, keyword index, proper name index, topic index, etc.

The index first appeared in the West, mainly the index of medieval European religious works. After the 18th century, the West began to have subject indexes. By the end of the 19th century, content analysis indexes were widely used. China's index appeared late. Generally believed that at the end of Ming

An index is a decentralized storage structure created to speed up the retrieval of rows of data in a table. An index is built for a table. It is composed of index pages other than data pages. Each index page contains logical pointers in order to speed up the retrieval of physical data. ^[2]

Indexing in a database system has the following functions:

(1) Get data quickly;

(2) Ensure the uniqueness of data records;

(3) to achieve referential integrity between tables;

(4) When using ORDER by and group by clauses for data retrieval, using indexes can reduce the time of sorting and grouping.

Depending on the capabilities of the database,

Not all databases use indexes in the same way. As a general rule, you need to create an index on a table only when you frequently query the data in the index column. Indexes take up disk space and reduce the speed of adding, deleting, and updating rows. If your application updates data very frequently or has limited disk space, you may need to limit the number of indexes. Create indexes when the table is large. The more data in the table, the more obvious the superiority of the index.

You can create an index based on a single column or multiple columns in a database table. Multi-column indexes allow you to distinguish rows where one of the columns may have the same value.

Indexes are also helpful if you often search two or more columns at the same time or sort by two or more columns. For example, if you often set criteria for both the first name and last name columns in the same query, it would make sense to create a multi-column index on those two columns.

Determine the validity of the index:

Check the WHERE and JOIN clauses of the query. Each column included in either clause is an object that the index can select.

Experiment with the new index to check its impact on running query performance.

Consider the number of indexes that have been created on the table. It is best to avoid having many indexes on a single table.

Check the definition of the indexes that have been created on the table. It is best to avoid overlapping indexes that contain shared columns.

Check the number of unique data values in a column and compare that number to the number of rows in the table. The result of the comparison is the selectivity of the column, which helps determine whether the column is suitable for indexing and, if appropriate, the type of index.