The answer is to create statistics on the columns used in WHERE clauses. This is correct because Azure Synapse Analytics serverless SQL pool relies on statistics to generate efficient query plans when querying external data like Parquet files; without them, the optimizer defaults to poor cardinality estimates, leading to slow joins and filters. On the Microsoft Azure Data Engineer Associate DP-203 exam, this concept tests your understanding of how serverless SQL pool differs from dedicated pools—specifically, that external data requires manual statistics creation for optimal performance. A common trap is assuming statistics are auto-created as in dedicated SQL pool, but serverless SQL pool does not maintain them automatically on external data. To remember, think: "Stats on WHERE, performance is there."
DP-203 Develop data processing Practice Question
This DP-203 practice question tests your understanding of develop data processing. 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 are using Azure Synapse Analytics serverless SQL pool to query Parquet files in Azure Data Lake Storage Gen2. The query performance is slow. Which action would most likely improve performance?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create statistics on the columns used in WHERE clauses
In Azure Synapse Analytics serverless SQL pool, query performance on external data like Parquet files heavily relies on statistics to enable the optimizer to generate efficient query plans. Without statistics, the engine makes default cardinality estimates, often leading to suboptimal joins and filters. Creating statistics on columns used in WHERE clauses allows the serverless SQL pool to accurately estimate row counts and choose better execution strategies, directly improving query performance.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Partition the Parquet files by date
Why it's wrong here
Partitioning helps if using partition elimination, but serverless SQL pool does not support it.
✗
Create a materialized view on the external data
Why it's wrong here
Materialized views are not supported in serverless SQL pool.
✗
Create a PolyBase external table and query that
Why it's wrong here
PolyBase is for dedicated SQL pool, not serverless.
✓
Create statistics on the columns used in WHERE clauses
Why this is correct
Statistics enable the optimizer to generate better execution plans.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume physical data organization (partitioning) or materialized views are the primary levers for performance in serverless SQL pool, overlooking that statistics are the critical metadata for the query optimizer in this stateless, compute-on-demand environment.
Detailed technical explanation
How to think about this question
Serverless SQL pool uses a distributed query engine that reads data directly from Azure Data Lake Storage Gen2 via the Hadoop Distributed File System (HDFS) driver. When statistics are missing, the engine defaults to a fixed row count estimate (e.g., 1,000 rows per partition), which can cause nested loop joins instead of hash joins, leading to severe performance degradation. In real-world scenarios, creating statistics on highly selective filter columns (e.g., customer_id or date) can reduce query times from minutes to seconds.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this DP-203 question in full detail.
Develop data processing — This question tests Develop data processing — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create statistics on the columns used in WHERE clauses — In Azure Synapse Analytics serverless SQL pool, query performance on external data like Parquet files heavily relies on statistics to enable the optimizer to generate efficient query plans. Without statistics, the engine makes default cardinality estimates, often leading to suboptimal joins and filters. Creating statistics on columns used in WHERE clauses allows the serverless SQL pool to accurately estimate row counts and choose better execution strategies, directly improving query performance.
What should I do if I get this DP-203 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Your team uses Azure Synapse Analytics serverless SQL pool to query Parquet files in Azure Data Lake Storage Gen2. The query performance is inconsistent, and some queries take a long time to execute. You need to improve query performance. What should you do?
hard
A.Increase the MAXDOP setting in the query
✓ B.Create statistics on the columns used in joins and filters
C.Move the data to a dedicated SQL pool
D.Convert the Parquet files to CSV format
Why B: Option B (Create statistics on the columns used in joins and filters) is correct because serverless SQL pool relies on statistics for optimal query plans. Option A (Increase the maximum degree of parallelism) is not directly applicable. Option C (Convert to CSV) would degrade performance. Option D (Use a dedicated SQL pool) may be an option but not the best immediate step.
Last reviewed: Jun 24, 2026
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