- dramatically improve read performance in [[Databases]] - otherwise there'd be huge latency searching the entire DB each time - but tradeoff is that this can slow write performance - types: ![[CleanShot 2025-02-28 at 16.50.44.png|400]] ![[CleanShot 2025-02-28 at 16.51.08.png|400]] - for faster search queries (such as searching for user's 1st name) ![[CleanShot 2025-02-28 at 16.51.57.png|400]] - useful for queries used on those columns togetherz