COF-C03 Data Loading, Unloading, and Connectivity Practice Question
A data engineer is troubleshooting a COPY INTO command that loads JSON files from a named external stage and is seeing unexpected NULL values in several VARIANT columns. Which TWO actions should the engineer take to diagnose how the JSON is being parsed? (Choose two.)
⚠ Common exam trap
The trap here is reaching for load-control options like ON_ERROR or structural options like STRIP_OUTER_ARRAY to investigate parsing problems, when validation and load-history views are the diagnostic tools.
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
✓
Run COPY INTO with VALIDATION_MODE = 'RETURN_ERRORS' to surface parsing problems before committing data.
Diagnosing unexpected NULLs in VARIANT columns requires visibility into how the load parsed the JSON. VALIDATION_MODE = 'RETURN_ERRORS' validates files and reports parsing errors without loading, while COPY_HISTORY provides per-statement load status and error details. Together they reveal whether the file format definition matches the actual JSON structure. Aborting the load, changing the format type, or stripping the outer array do not expose the parsing problem.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enable STRIP_OUTER_ARRAY = TRUE on the file format to flatten the JSON into columns.
Why it's wrong here
STRIP_OUTER_ARRAY removes the enclosing array so each element becomes a separate row; it does not flatten objects into columns nor explain why individual paths are NULL. It is a legitimate JSON loading option but unrelated to diagnosing unexpected NULLs. Setting it without understanding the source structure could change row counts rather than reveal the parsing fault.
- ✓
Run COPY INTO with VALIDATION_MODE = 'RETURN_ERRORS' to surface parsing problems before committing data.
Why this is correct
VALIDATION_MODE = 'RETURN_ERRORS' validates files against the specified file format and returns any parsing errors without loading data, which directly exposes mismatches such as incorrect field or record delimiters causing NULL VARIANT values. This is the recommended way to test a file format against real files before a production load, and it aligns with diagnosing JSON parsing behavior.
- ✗
Set ON_ERROR = 'ABORT_STATEMENT' and rerun the load to force Snowflake to reveal the malformed records.
Why it's wrong here
ABORT_STATEMENT simply halts the load when an error occurs; it does not report which JSON elements failed to parse or why VARIANT columns became NULL. The statement fails without the detailed diagnostics needed to understand parsing behavior. It is a load-control setting rather than a diagnostic facility, so it does not help identify the cause of the NULLs.
- ✗
Change the file format TYPE to CSV so Snowflake parses each line as a flat record and exposes the raw text.
Why it's wrong here
Switching the file format to CSV misinterprets JSON content and would produce different, unrelated parsing errors instead of clarifying the VARIANT issue. The scenario concerns JSON parsing, so altering the format type changes the semantics entirely. It does not surface the underlying problem and risks corrupting how the data is interpreted.
- ✓
Query the COPY_HISTORY ACCOUNT_USAGE view to review the load status and error details for recent COPY statements.
Why this is correct
The COPY_HISTORY view in the ACCOUNT_USAGE schema records each COPY statement with row counts, error limits, and status, helping confirm whether rows loaded or were partially rejected. Reviewing it reveals whether the NULLs stem from parse failures recorded during the load. It is a documented diagnostic surface for load activity and complements inspecting the raw JSON itself.
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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.