Covered Query - response (1) by dnoeth

Hi Rajeev,
a Covering Index means that all of the columns needed to process a query are included in an existing index.
The optimizer can use this index instead of scanning the base table, which usually results in less IOs -> faster query.

It might be a NUSI (simple case, only a single table is used in query) or a Join Index (complex case, multiple tables plus aggregation possible). Creating an index specifically for query covering is mainly useful if you got a set of predefined queries with a large number of executions.

Dieter