DP-300 Practice Question: Monitor, configure, and optimize database resources
You manage an Azure SQL Database (General Purpose, S2) used by a reporting application. The database has a table `FactSales` with 500 million rows. Queries that aggregate sales by date are slow. The execution plan shows a clustered index scan on `FactSales`. The table has a clustered index on `SaleID` and a nonclustered index on `DateKey`. The queries filter by `DateKey` and `ProductKey`. You need to improve query performance without changing the service tier. Which action should you take?
⚠ Common exam trap
Many candidates choose partitioning (Option B) thinking it speeds up all queries by date, but without a covering index, partitioning alone does not eliminate the scan; it only reduces the data scanned to a single partition.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a covering index on DateKey and ProductKey including the aggregated columns.
The query filters by DateKey and ProductKey and aggregates sales data. A covering index on DateKey and ProductKey that includes the aggregated columns (e.g., SUM(SalesAmount)) allows the query to be satisfied entirely from the index without touching the clustered index, eliminating the costly clustered index scan. This is the most direct and effective way to improve performance without changing the service tier.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Create a nonclustered index on ProductKey only.
Why it's wrong here
ProductKey index alone does not cover the query.
- ✗
Partition the table by DateKey.
Why it's wrong here
Partitioning does not guarantee index seeks.
- ✗
Create a clustered columnstore index on the table.
Why it's wrong here
Columnstore is for DW, not OLTP.
- ✓
Create a covering index on DateKey and ProductKey including the aggregated columns.
Why this is correct
Covering index provides index seeks and avoids lookups.
Go deeper
Related to this question
Learn chapter
Overview of Azure Data Platform Options
Key term
Azure SQL Indexes
Structures in Azure SQL Database that speed up data retrieval by providing quick access paths to rows, similar to a book index.
Key term
Azure SQL Performance Tuning
Azure SQL Performance Tuning is the process of optimizing the speed and efficiency of queries and database operations in Microsoft Azure SQL Database or SQL Managed Instance to reduce latency and improve throughput.
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