What is a partial index?

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An index built over only the rows matching a WHERE clause — smaller and cheaper to maintain — CREATE INDEX ... WHERE status = 'active' indexes just the matching rows — ideal when queries target a small hot subset. Column selection is simply a normal index's column list, PostgreSQL builds indexes in one operation (CONCURRENTLY changes locking, not scheduling), and prefix truncation describes MySQL's prefix indexes.

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An index covering only a subset of the table's columns — the others remain unindexed

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An index that is built gradually during idle periods — construction pauses under load

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An index storing only truncated key prefixes — longer values are cut to save space

What is a partial index?

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