What does primary mean in mysql?

The PRIMARY keyword in MySQL is used to specify the primary key, uniquely identifying each row of records to ensure data integrity and consistency. The functions of the primary key include uniquely identifying records, serving as an index to improve query efficiency, and maintaining data integrity. When creating a primary key, the column value must be unique and cannot be NULL, and the primary key cannot be modified or deleted. Other types of keys in MySQL, such as unique keys and foreign keys, ensure unique column values ​​and establish relationships between tables, respectively. The advantages of using primary keys include improving query efficiency, ensuring data integrity, and simplifying data operations.

The meaning of PRIMARY in MySQL

In MySQL, PRIMARY is a keyword used to specify the table One or more columns serve as the primary key. The primary key uniquely identifies each row of records in a table and ensures data integrity and consistency.

The role of the primary key

The primary key has the following functions:

• Uniquely identifies each record in the table to prevent data duplication.
• Used as an index to improve the efficiency of query and update operations.
• Maintain data integrity by ensuring that the primary key is always used when looking up and updating records in the table.

Creating a primary key

When creating a table, you can use the following syntax to create a primary key:

<code class="sql">CREATE TABLE table_name (
  column_name1 data_type PRIMARY KEY,
  column_name2 data_type,
  ...
);</code>

Where:

• column_name1 is the column name used as the primary key.
• data_type is the data type of the column.

Constraints of the primary key

The primary key has the following constraints:

• The value must be unique, that is, there cannot be two records in the table Have the same primary key value.
• Value cannot be NULL.
• The primary key column cannot be modified or deleted.

The difference between primary keys and other keys

There are other types of keys in MySQL, such as unique keys (UNIQUE) and foreign keys (FOREIGN KEY). The difference between the primary key and other keys is as follows:

• Unique key: ensures that the values ​​in the column are unique, but allows NULL values.
• Foreign key: used to establish a relationship between two tables to ensure that the value in one table exists in the other table.

Advantages of using primary keys

The advantages of using primary keys include:

• Improving query efficiency because MySQL can use primary keys as Index to find data quickly.
• Ensure data integrity and prevent the insertion of duplicate records.
• Simplify data operations such as updating or deleting records.

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