Database Management Systems · Storage and query processing

Index selectivity

How narrowly a condition filters the table, the reason a low-selectivity index gets ignored in favor of a full scan.

Also known as: cardinality estimation, when the planner skips an index.

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• Indexes and B-trees: A sorted, tree-shaped shortcut structure that lets the database find rows without scanning the whole table.

Related topics

• Query processing and optimization: How the database decides which order to run joins and filters in, to answer a query as cheaply as possible.