How can I leverage indexes in MySQL view queries to improve performance?

Using Indexes in MySQL View Queries

Issue:

You're encountering performance issues with a MySQL view because the index on a underlying table is not used in view-based queries.

原因:

MySQL does not push filter predicates (e.g., WHERE happened_in = 2006) from outer queries into view queries. Instead, it materializes the view results as an intermediate temporary table and applies the predicate to this table. As a result, indexes on the original table cannot be used effectively.

Solution:

To leverage indexes in view queries, you need to create a suitable index that can be used by the view query. In this case, a covering index that includes all columns referenced in the view query is recommended.

Optimum Index:

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

Why it Works:

• The player column is used as the leading column because of the equality predicate WHERE player = 24.
• The happened_in column is the second leading column due to the GROUP BY happened_in.
• The inclusion of the score column makes the index a covering index, enabling MySQL to satisfy the query from index pages without accessing the data pages.

Additional Considerations:

• You can compare the execution plan of the view query to a standalone query without a view to see the performance difference.
• While using views in MySQL is not necessarily harmful, it's crucial to understand how MySQL processes view queries to avoid performance issues.

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