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A composite index is a database index that encompasses multiple columns, offering efficient lookup performance when queries involve multiple columns. It's a powerful tool that can significantly enhance database performance, but its application should be meticulously considered to maximize its benefits.
Composite indexes are ideal when:
Composite indexes offer significant performance advantages but also come with some trade-offs:
In your example, where you have a homes table with columns such as geolat, geolng, sqft, and year_built, a composite index on (geolat, geolng) will be beneficial if you frequently execute queries that filter or join based on both location coordinates.
Query with Composite Index:
SELECT * FROM homes WHERE geolat BETWEEN ... AND ... AND geolng BETWEEN ... AND ...
This query will leverage the composite index (geolat, geolng) to efficiently filter based on both location coordinates, resulting in faster execution.
Query without Composite Index:
SELECT * FROM homes WHERE geolat = ... AND geolng = ...
Without the composite index, the database must perform a full table scan to retrieve the matching records, leading to slower execution.
In your updated scenario, with the additional schema and query details, the composite index on (geolat, geolng) is still recommended. The EXPLAIN output indicates that the query is utilizing the existing single-column indexes on geolat and geolng but is not combining them for range filtering. A composite index on both columns would combine them and potentially further optimize the query performance.
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