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

Understanding the Differences between INDEX, PRIMARY, UNIQUE, and FULLTEXT in MySQL

When creating tables in MySQL, it's crucial to understand the distinctions between different types of indexes. Four key index types exist:

1. INDEX (or KEY):

A non-unique index allows duplicate values and is used solely for optimization. It speeds up data retrieval but doesn't enforce any constraints.

2. UNIQUE:

A unique index ensures that all values in the index are unique. It prevents duplicate entries and can also be used for optimization. However, it allows NULL values, which may result in duplicates.

3. PRIMARY:

A primary index acts like a unique index but restricts NULL values. It serves as the primary means of uniquely identifying rows in a table. It should be defined on the minimum number of columns necessary to ensure uniqueness. In InnoDB tables, the primary index stores the actual table data internally.

4. FULLTEXT:

A full-text index is specialized for full-text searches using the MATCH() / AGAINST() syntax. Unlike other indexes, it doesn't improve performance for other types of queries and is only relevant for searching text data.

Similarities:

• All index types can include multiple columns.
• The order of columns in an index is crucial for efficient querying, with the leftmost columns being used first.
• A FULLTEXT index, however, requires all columns to be used in a query to be effective.

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