What is the index of access?

In an access relational database, an index is a separate, physical storage structure in a relational database that sorts the values ​​of one or more columns in a database table. It is a collection of one or several column values ​​in a table and the corresponding list of logical pointers pointing to the physical identifiers in the table and the data pages of these values.

The index is equivalent to the table of contents of the book. You can quickly find the required content based on the page numbers in the table of contents.

Indices provide pointers to data values ​​stored in specified columns of a table, and then sort these pointers according to the sort order you specify. The database uses an index to find a specific value and then points forward to find the row containing that value. This allows SQL statements corresponding to the table to execute faster and allows quick access to specific information in the database table.

When there are a large number of records in the table, if you want to query the table, the first way to search for information is to search the whole table, which is to take out all the records one by one, compare them one by one with the query conditions, and then return Records that meet the conditions will consume a lot of database system time and cause a lot of disk I/O operations; the second is to create an index in the table, then find the index value that meets the query conditions in the index, and finally save it in the index The ROWID (equivalent to the page number) in the table can quickly find the corresponding record in the table.

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