Home > Database > Mysql Tutorial > body text

Can mysql primary key be empty?

藏色散人
Release: 2020-09-14 15:19:07
Original
22286 people have browsed it

mysql primary key cannot be empty, because when creating or changing a table, you can create a primary key by defining a "PRIMARY KEY" constraint, and a table can only have one primary key constraint, and the columns in the primary key constraint cannot be empty. Value, because primary key constraints ensure unique data, identity columns are often defined.

Can mysql primary key be empty?

The database primary key refers to a column or a combination of columns in the table, and its value can uniquely identify each row in the table. Such a column or columns become the primary key of the table, through which the entity integrity of the table is enforced. When creating or changing a table, you can create a primary key by defining a PRIMARY KEY constraint. A table can only have one primary key constraint, and the columns in the primary key constraint cannot be null. Since the primary key constraint ensures unique data, identity columns are often defined. .

The role of the primary key:

1. As can be seen from the above definition, the primary key is used to uniquely identify a row of data in the database table.

2. As an object that can be effectively referenced by foreign keys.

Can the mysql primary key be empty?

Attention! The primary key can never be null!

The above is the detailed content of Can mysql primary key be empty?. For more information, please follow other related articles on the PHP Chinese website!

Related labels:
source:php.cn
Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Popular Tutorials
More>
Latest Downloads
More>
Web Effects
Website Source Code
Website Materials
Front End Template