The role of primary key in mysql

The primary key in MySQL is a column or column combination that uniquely identifies each row in the table. The main functions include: 1. Unique constraints: ensure that each row has a unique value; 2. Optimize query performance: serve as an index to improve query and sorting speed; 3. Foreign key reference: establish relationships between tables; 4. Auto-increment: insert Automatically generate unique consecutive integers when creating new rows; 5. Table constraints: limit data integrity and prevent duplicate values.

The role of primary key in MySQL

Introduction
primary key（ A primary key) is a combination of one or more columns in a MySQL table that uniquely identifies each row in the table.

Function

1. Unique constraint:
primary key ensures that each row in the table has a different value, thus Ensure data uniqueness.

2. Optimize query performance:
MySQL uses primary key as an index to quickly find specific rows, thus improving query and sorting performance.

3. Foreign key reference:
The primary key can be referenced by foreign keys in other tables to establish relationships between tables and maintain data integrity and consistency.

4. Auto-increment:
The primary key is usually set as the primary key auto-increment column. When a new row is inserted, MySQL will automatically generate a unique and continuous column for it. integer.

5. Table constraints:
Primary key is a type of table constraint that can be used to limit the integrity of data, such as ensuring that data will not be duplicated when inserting or updating. value.

Configuration

When creating a table, you can specify the primary key through the following syntax:

<code>CREATE TABLE table_name (
  primary_key_column_name data_type PRIMARY KEY
);</code>

Usage example

<code>CREATE TABLE users (
  id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(255) NOT NULL
);</code>

In this example, the id column is set as the primary key, which is an auto-incrementing integer that uniquely identifies each user.

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