Quick Answer
The answer is to create a clustered columnstore index on the table. This is correct because a clustered columnstore index stores data in a columnar format, which dramatically reduces the number of pages read for queries filtering by customer ID, thereby lowering IO and eliminating the expensive key lookups that occur when a nonclustered index on customer ID must fetch additional columns from the clustered index. On the DP-300 exam, this scenario tests your understanding of when to choose columnstore over traditional rowstore indexes for large analytical or mixed workloads, with a common trap being to add included columns to the existing nonclustered index—this bloats storage and still requires lookups for columns not covered. Remember the memory tip: “Columnstore crushes costly key lookups” by storing all needed columns in the same compressed structure, making it ideal for optimizing a large table with key lookups in Azure SQL Database.
This DP-300 practice question tests your understanding of monitor, configure, and optimize database resources. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You administer a large Azure SQL Database that is used for a SaaS application. The database has a table with over 1 billion rows that is frequently queried by customer ID. The table currently has a clustered index on an identity column and a nonclustered index on customer ID. Queries that filter by customer ID are experiencing high IO and long execution times. You analyze the execution plan and see that the nonclustered index is used, but there are many key lookups. You need to optimize the query performance while minimizing storage overhead. What should you do?
Create a clustered columnstore index on the table
Reduces IO and storage; eliminates lookups.
Create a filtered index on customer ID for frequent values
Why wrong: Not practical for many different IDs.
Partition the table by customer ID
Why wrong: Does not reduce IO for point queries.
Add all queried columns as included columns to the nonclustered index
Why wrong: Increases storage and maintenance overhead.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Create a clustered columnstore index on the table
Option A is correct because creating a clustered columnstore index on the table will significantly reduce IO by using columnar storage and eliminate key lookups; it also provides high compression to minimize storage. Option B is wrong because adding included columns to the nonclustered index will increase storage size and may not fully eliminate lookups. Option C is wrong because partitioning by customer ID can improve maintenance but may not reduce IO for point queries. Option D is wrong because creating a filtered index on customer ID is not helpful for many different customer IDs.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Create a clustered columnstore index on the table
Why this is correct
Reduces IO and storage; eliminates lookups.
Related concept
Static NAT maps one inside address to one outside address.
Create a filtered index on customer ID for frequent values
Why it's wrong here
Not practical for many different IDs.
Partition the table by customer ID
Why it's wrong here
Does not reduce IO for point queries.
Add all queried columns as included columns to the nonclustered index
Why it's wrong here
Increases storage and maintenance overhead.
Common exam traps
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DP-300 NAT questions on configuration and troubleshooting.
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FAQ
Monitor, configure, and optimize database resources — This question tests Monitor, configure, and optimize database resources — Static NAT maps one inside address to one outside address..
The correct answer is: Create a clustered columnstore index on the table — Option A is correct because creating a clustered columnstore index on the table will significantly reduce IO by using columnar storage and eliminate key lookups; it also provides high compression to minimize storage. Option B is wrong because adding included columns to the nonclustered index will increase storage size and may not fully eliminate lookups. Option C is wrong because partitioning by customer ID can improve maintenance but may not reduce IO for point queries. Option D is wrong because creating a filtered index on customer ID is not helpful for many different customer IDs.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DP-300 NAT questions on configuration and troubleshooting.
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 21, 2026
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