Answer
A covering index contains all columns needed for a query. It removes key lookups and improves performance in read-heavy workloads.
Quick Answer
A covering index satisfies a query entirely from the index without touching the main table. Include the WHERE columns as index keys and extra SELECT columns via INCLUDE. Eliminates costly key lookups. One well-placed covering index can eliminate 90% of I/O for frequently-run queries.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ