COF-C03 Practice Question: Performance Optimization, Querying, and Transformation
Which function should be used to transform a single row containing a semi-structured VARIANT column with an array of objects into multiple individual rows?
⚠ Common exam trap
Candidates often confuse FLATTEN with PARSE_JSON or GET. While those functions access data, only FLATTEN is specifically designed to transform nested arrays into a relational set of 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
✓
FLATTEN
Transforming semi-structured data is a core capability of Snowflake, allowing users to convert nested JSON or arrays into a relational format. The FLATTEN function is specifically designed for this purpose, enabling data analysts to join the parent row with its child elements, which is essential for reporting and traditional SQL analysis.
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 is used to convert a string into a VARIANT data type so that Snowflake can interpret the semi-structured content. It does not perform any structural transformation or row expansion; it merely prepares the data for other functions like FLATTEN or simple dot-notation traversal.
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OBJECT_CONSTRUCT
Why it's wrong here
OBJECT_CONSTRUCT is used to take individual relational columns and combine them into a single JSON object. This is the opposite of what the question asks, as it aggregates data into a semi-structured format rather than expanding an array into multiple individual rows.
- ✓
FLATTEN
Why this is correct
The FLATTEN function takes a semi-structured column (like an array or object) and explodes it into multiple rows. Each element of the array becomes its own row in the result set, which can then be queried using standard SQL, making it the standard tool for unnesting data.
- ✗
STRIP_NULL_VALUE
Why it's wrong here
STRIP_NULL_VALUE is a utility function used to remove JSON null values from a VARIANT column. It helps clean up semi-structured data by converting JSON 'null' into SQL NULL, but it has no impact on the number of rows or the expansion of arrays.
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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
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