How to use primary key in mysql

The primary key is used in MySQL to uniquely identify each record in the table, ensure uniqueness and fast search, and is used as the basis for foreign key reference and constraint maintenance.

The purpose of primary key in MySQL

The primary key, also known as the primary keyword, is the primary key in MySQL. A special column that uniquely identifies each record in the table. The primary key value must be unique and non-null in the table.

The role of the primary key

• Uniqueness guarantee: The primary key value ensures that no two records in the table have the same value.
• Fast search: The primary key is used to create an index so that records can be found quickly and efficiently.
• Foreign key reference: The primary key value is used as a foreign key to other tables to establish relationships and ensure data integrity.
• Constraint maintenance: The primary key restricts the insertion of duplicate values ​​into the table, thereby ensuring the accuracy of the data.

How to specify the primary key

When creating a table, you can use the PRIMARY KEY constraint to specify the primary key. Here is the syntax:

<code>CREATE TABLE table_name (
  column1 data_type,
  column2 data_type,
  ...
  PRIMARY KEY (column_name)
)</code>

where column_name is the name of the column you want to designate as the primary key.

Types of primary keys

MySQL supports the following types of primary keys:

• Single field primary key: Only one column as primary key.
• Composite primary key: Multiple columns are combined together as the primary key.
• Auto-increment primary key: MySQL automatically generates a unique identifier.

Notes

• Ensure that the primary key value is always unique and non-null.
• Avoid using duplicate values ​​or values ​​that may change over time as primary keys.
• Changing the primary key may affect the performance and integrity of the database.

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