COF-C03 Practice Question: Performance Optimization, Querying, and Transformation
A data engineer needs to transform semi-structured data stored in a VARIANT column that contains an array of JSON objects into a relational table with one row per object. The engineer wants to use a Snowflake function that can expand the array into multiple rows. Which function should be used?
⚠ Common exam trap
A common mix-up: candidates confuse functions that manipulate semi-structured data with the one that specifically expands arrays into rows.
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
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FLATTEN
FLATTEN is the correct function to expand an array of objects into multiple rows. It is typically used in the FROM clause with LATERAL, allowing each element of the array to become a separate row while preserving access to the original row's columns. The other functions either create VARIANT values or aggregate rows, not expand arrays.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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PARSE_JSON
Why it's wrong here
PARSE_JSON converts a string containing JSON into a VARIANT value. It does not expand arrays or create multiple rows. In this scenario, the data is already in VARIANT format, so PARSE_JSON would not help transform the array into rows; it would only reinterpret a string as VARIANT.
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FLATTEN
Why this is correct
FLATTEN is a table function that takes a VARIANT column and expands arrays or objects into multiple rows. It is designed exactly for this purpose, producing one row per element in the array. Using LATERAL FLATTEN allows the engineer to join the expanded rows back to the original table, achieving the desired relational format.
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OBJECT_CONSTRUCT
Why it's wrong here
OBJECT_CONSTRUCT creates a JSON object from key-value pairs. It is used for building objects, not for expanding an existing array into rows. Applying it here would not produce one row per array element and would not achieve the required relational transformation.
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ARRAY_AGG
Why it's wrong here
ARRAY_AGG is an aggregation function that collects values into an array. It performs the opposite operation of what is needed: it groups rows into an array rather than expanding an array into rows. Using it would not transform the semi-structured array into a relational format.
About these practice questions
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Snowflake exam blueprint
This COF-C03 practice question is part of Courseiva's free Snowflake certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the COF-C03 exam.