DP-300 Certification Practice Question #179

Question

You have an Azure SQL database.
You have a query and the associated execution plan as shown in the following exhibit.

Use the drop-down menus to select the answer choice that completes each statement based on the information presented in the graphic.
NOTE: Each correct selection is worth one point.
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Accepted Answer

The execution plan shows that the `Key Lookup` operator is responsible for 99% of the overall query cost, identifying it as the main performance bottleneck. A Key Lookup occurs when the query optimizer uses a nonclustered index to locate records (in this case, via `Index Seek` on `ModifiedDate`) but must subsequently lookup the remaining columns from the clustered index (the table itself). To resolve this performance issue, you can convert the nonclustered index into a covering index by adding the missing columns to the `INCLUDE` clause of the nonclustered index, eliminating the need for a clustered key lookup.

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