Answer
A covering index contains all columns needed for a query.
SQL Server can return results from the index alone without touching the table.
This greatly improves performance for read-heavy queries.
Quick Answer
A covering index includes all the columns a query needs — the index columns plus extra INCLUDE columns. SQL Server can answer the query entirely from the index without touching the main table. Eliminates key lookups, reduces I/O, and often cuts query time dramatically.
S
SugharaIQ Editorial Team
Verified Answer
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Source: SugharaIQ