Programming terminology uses indexes to quickly access specific information in database tables. An index is a structure that sorts the values of one or more columns in a database table, such as the last lname column in the employee table. If you want to find a specific employee by last name, the index will help you get this information faster than if you have to search all the rows in the table.
An index provides pointers to data values stored in a specified column of a table, and then sorts these pointers according to the sort order you specify. A database uses an index in a way similar to the way you use an index in a book: it searches the index for a specific value, and then follows the pointer to find the row containing that value.
In the database diagram, you can create, edit or delete each index type in the index/key property page of the selected table. When you save a table with an index attached or a chart where the table is located, the index will be saved in the database.
Note that not all databases use indexes in the same way. Generally speaking, you only need to create an index on the table when you frequently query the data in the index column. Indexes take up disk space and slow down the speed of adding, deleting and updating rows. In most cases, the speed advantage of index in data retrieval greatly exceeds its shortcomings. However, if your application updates data very frequently or disk space is limited, you may need to limit the number of indexes.
You can create an index based on one or more columns in a database table. A multi-column index allows you to distinguish rows in which one column may have the same value.
Indexes are also helpful if you often search or sort by two or more columns at the same time. For example, if you often set conditions for last name and first name columns in the same query, it makes sense to create a multi-column index on these two columns.
Determine the effectiveness of the index:
Check the WHERE and JOIN clauses of the query. Every column contained in any clause is an object that can be selected by the index.
Experiment with the new index and check its impact on the performance of running queries.
Consider the number of indexes that have been created on the table. It is best to avoid having many indexes on a table.
Check the definition of the index that has been created on the table. It is best to avoid overlapping indexes that contain * * * columns.
Check the number of unique data values in the column and compare it with the number of rows in the table. The result of the comparison is the selectivity of the column, which helps to determine whether the column is suitable for the index and, if so, the type of the index.
Publish an index of terms, that is, research. It records the words, words, sentences, names, places, names and themes in books or newspapers into concise entries, indicates their origins and page numbers, and arranges them into books according to certain retrieval methods. It is time-consuming and laborious for us to find a name from a large set of books. Thousands of newspapers and periodicals are like looking for a needle in a haystack to find information on a specific topic. If you use an index, you can get it through books. It not only saves time, but also helps to understand the academic development trend.
Indexes are divided into two categories. One is book index, which is divided into sentence index, subject index, article title index, name index and so on according to the object of index; Secondly, there are two kinds of newspaper indexes: comprehensive and special, such as national newspaper information index and national newspaper literature and paper index.
The indexes are arranged according to the theme and some according to the stroke order. Be sure to read the arrangement instructions before use, so as to be free.