What is the word primary key in mysql?

In MySQL, the primary key is a column or column group that uniquely identifies each record in the table. It has the characteristics of uniqueness, non-nullability, and mandatory. It is used to ensure data integrity, quickly search for data, and establish external databases. key relationship. You can set the primary key like this: ALTER TABLE table name ADD PRIMARY KEY (column name).

Primary key in MySQL

In MySQL, the primary key (Primary Key) is a unique identifier for each item in a database table. A column or set of columns for records.

Features and functions:

• Uniqueness:The value in the primary key must be unique, that is, there are no two records in the table Have the same primary key value.
• Non-nullability: Primary keys are usually not allowed to be NULL values ​​to ensure record identifiability.
• Mandatory: Most database management systems (including MySQL) force the primary key to be defined when the table is created.

Benefits:

• Ensure data integrity: Primary keys help prevent the insertion of duplicate records, thereby maintaining data accuracy.
• Find data quickly: The database uses the primary key as an index to find records quickly and efficiently.
• Foreign key relationship: The primary key can be used as a reference object for foreign keys in other tables to establish relationships between data.

How to set the primary key:

In MySQL, use the PRIMARY KEY constraint to define the primary key. The syntax is as follows:

<code>ALTER TABLE table_name ADD PRIMARY KEY (column_name);</code>

For example:

<code>ALTER TABLE customers ADD PRIMARY KEY (customer_id);</code>

This will set a primary key constraint on the customer_id column in the customers table.

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