Can MySQL Views Leverage Index Enhancements for Improved Performance?

Is the Use of MySQL Views a Detrimental Practice?

Despite advice suggesting the contrary, views can indeed leverage index enhancements when used within MySQL. The question arises as to how such functionality may be implemented.

The Answer: Providing Suitable Indices

The solution lies in offering an index that MySQL can actively utilize. In this case, a "covering" index is most appropriate, such as:

CREATE INDEX highscores_IX3 ON highscores (player, happened_in, score)

With this index in place, MySQL's optimizer should be able to employ it for the SELECT query, resulting in an "Using index" declaration attributable to the WHERE player = 24 predicate.

However, it is essential to acknowledge that MySQL is unlikely to utilize a happened_in index for view queries due to its behavior of separating inner "view query" executions from outer queries. Consequently, the index defined for happened_in will not be utilized during the query formation phase.

Performance Optimization with a Covering Index

To optimize view query performance, a "covering index" that includes all columns referenced in the query (e.g., ON highscores (player, happened_in, score)) is recommended. This type of index enables direct data retrieval from index pages without the need for page lookups in the underlying table, resulting in an "Using index" access method.

Comparison to a Standalone Query with no Derived Table

For comparison, consider a standalone query equivalent to the view query:

SELECT player, MAX(score) AS highest_score, happened_in
FROM highscores
WHERE player = 24 AND happened_in = 2006
GROUP BY player, happened_in

A covering index for this query (e.g., ON highscores (player, happened_in, score)) can also be utilized, eliminating the need for an intermediate "derived" table.

Caution and Considerations

While views are not inherently detrimental, it is crucial to understand how MySQL processes view queries, which differs from the approaches adopted by other databases. This knowledge enables developers to effectively harness the potential of views while mitigating performance pitfalls.

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