Shulou(Shulou.com)06/02 Report--

This article mainly explains the "MySQL, index, primary key, unique index, joint index difference", the article explains the content is simple and clear, easy to learn and understand, the following please follow the editor's ideas slowly in-depth, together to study and learn "MySQL, index, primary key, unique index, joint index of the difference" bar!

Indexes are special files (indexes on InnoDB data tables are part of the table space) that contain reference pointers to all records in the data table.

The only task of a normal index (an index defined by the keyword KEY or INDEX) is to speed up access to data.

A normal index allows indexed data columns to contain duplicate values. If you can be sure that a data column will contain only these different values, you should define it as a unique index with the keyword UNIQUE when you create an index on that data column.

In other words, the unique index can guarantee the uniqueness of the data record.

A primary key is a special unique index. Only one primary key index can be defined in a table. The primary key is used to identify only one record and is created using the keyword PRIMARY KEY.

An index can overwrite multiple data columns, such as an INDEX (columnA, columnB) index, which is a federated index.

Indexing can greatly improve the query speed of data, but it will slow down the speed of inserting, deleting, and updating tables, because index files have to be manipulated when performing these write operations.

Thank you for your reading, the above is the "MySQL, index, primary key, unique index, joint index difference" of the content, after the study of this article, I believe you on the MySQL, index, primary key, unique index, joint index of the difference between this issue has a deeper understanding, the specific use of the need for practice to verify. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.