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Databases

Composite index

An index over several columns, usable for queries filtering on a leftmost prefix of them.

The leftmost-prefix rule is the whole question. An index on (a, b) helps WHERE a = ? and WHERE a = ? AND b = ?, but not WHERE b = ?.

An index containing every column a query needs, so the engine never reads the table itself.

A predicate that can use an index seek - the indexed column appears bare, not wrapped in a function.

This term is part of the free Python Full-Stack interview preparation module - browse the full glossary for every definition.

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