What is the primary key in mysql

The primary key is a column or column combination that uniquely identifies each row in the MySQL table, ensuring data uniqueness and preventing duplication. Characteristics include: 1. Uniqueness: the primary key value is unique in the table; 2. Non-null: the primary key column cannot be NULL; 3. Immutable: the primary key value cannot be changed once assigned. The functions are: 1. Uniquely identifying rows; 2. Optimizing data retrieval and update; 3. Establishing relationships between tables.

What is a primary key in MySQL?

The primary key is a column or combination of columns that uniquely identifies each row in a MySQL database table. It is a constraint that ensures that each row's value is unique, thus preventing data duplication.

Characteristics of primary key:

• Uniqueness: The primary key value must be unique in the table.
• Non-empty: The primary key column cannot be NULL.
• Immutable: Once a primary key value is assigned, it cannot be changed.

The role of the primary key:

• Uniquely identifies each row in the table.
• Optimize data retrieval and update.
• Establish relationships between tables.

Create a primary key:

When creating a table, you can use the PRIMARY KEY constraint to specify the primary key. For example:

<code class="sql">CREATE TABLE my_table (
  id INT NOT NULL PRIMARY KEY,
  name VARCHAR(255)
);</code>

This will create a primary key column named id in the table named my_table.

Note:

• The primary key can be a single column or a combination of multiple columns.
• For a table, only one primary key can be defined.
• The primary key should select columns with high selectivity, that is, columns that contain unique values.

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