Does MySQL Automatically Index Foreign Key Columns?

Does MySQL Index Foreign Key Columns Implicitly?

MySQL does not automatically create indexes on foreign key columns, except when using the InnoDB storage engine. InnoDB is the only table format in MySQL that supports foreign key constraints and their indexing.

Foreign keys are used to establish relationships between rows in different tables, ensuring data integrity and referential consistency. By default, MySQL only creates indexes on primary and unique key columns, but it does not automatically index foreign keys.

To explicitly create an index on a foreign key column, the following syntax can be used:

ALTER TABLE `table_name` ADD INDEX (`foreign_key_column`);

Indexing foreign key columns can significantly improve the performance of queries and joins involving these relationships. By creating an index on a foreign key column, MySQL can quickly locate the rows in the referenced table, avoiding full table scans.

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