What are the Differences and Similarities Between INDEX, PRIMARY, UNIQUE, and FULLTEXT Indexes in MySQL?

Understanding INDEX, PRIMARY, UNIQUE, and FULLTEXT in MySQL

MySQL provides various index types to optimize data retrieval and ensure data integrity. These index types differ in their capabilities and usage scenarios.

Differences:

• INDEX or KEY: A non-unique index that allows duplicate values. Used solely for enhancing data access speed.
• UNIQUE: An index that enforces uniqueness, ensuring that each row in the index has distinct non-NULL values for all columns. Can also be used to enforce data constraints.
• PRIMARY: Similar to UNIQUE, but always named 'PRIMARY' and can only be present once per table. Intended for uniquely identifying table rows and should not allow NULL values.
• FULLTEXT: Specialized for full-text searches using the MATCH() / AGAINST() clause. Differs significantly from other index types in its narrow purpose.

Similarities:

• All index types can contain multiple columns.
• The order of columns in an index is crucial for efficient querying. Queries must use columns from the left starting from the indexed columns.
• FULLTEXT indexes, however, require all columns to be used for querying.

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