When to Use KEY, PRIMARY KEY, UNIQUE KEY, and INDEX in MySQL?

When to Use KEY, PRIMARY KEY, UNIQUE KEY, and Index in MySQL

Databases rely on indexes to enhance data retrieval efficiency, especially for columns utilized in JOIN, WHERE, and ORDER BY operations.

KEY and INDEX: Synonymous Terms

In MySQL, KEY and INDEX are interchangeable terms. They both refer to a mechanism that accelerates data retrieval by allowing quick navigation to specific data pages. This process resembles flipping through a phone book directory to find a specific last name by section, rather than methodically searching page by page.

Primary Key vs. Unique Key

Primary and unique keys share common characteristics. Both ensure that each table row possesses a unique identifier, whether through a single column or a combination of columns. The primary key is a particular type of unique key.

Table Structure Restrictions

A table can only have a single primary key but may possess multiple unique keys. Additionally, primary and unique key columns are automatically indexed in MySQL, further enhancing retrieval speed.

Choosing the Appropriate Option

• Use KEY / INDEX to index frequently used columns, maximizing data retrieval efficiency.
• Employ PRIMARY KEY to establish a unique identifier for each row in a table.
• Opt for UNIQUE KEY to impose the uniqueness constraint on specific columns, ensuring no two rows possess identical values for those columns.

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