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Research Note Description:
Snapshots are much like executing a query but still there are exceptions. Snapshots have common points as ‘view’ but not the same thing as 'view'. They are real not virtual unlike 'view'. Their own separately materialized copy of the data defines them. Snapshots represents the relevant data as it was at most 24 hours ago…
Exceptions of snapshots not being much like a query are:
a) The result of a query in the database under the specified name as a read-only relvar.
b) Periodically the snapshot is refreshed. That means the current value is discarded. And when it is executed again – the result is new snapshot after the execution.
For example: VAR JAS SNAPSHOT ((S JOIN SP) WHERE P#=P# (‘P2’)) {S#, CITY} REFRESH EVERYDAY;
The above query means: The query has specified name JAS and some conditions for snapshot to be made, and REFRESH EVERYDAY means that whenever it is refreshed snapshot gets a new snapshot value.
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Prof. Ashay Dharwadker