DEA-C02 Data Transformation Practice Question
A data engineer is converting a column of strings into integers. Some rows contain non-numeric characters that would normally cause the query to fail. Which function should be used to return a NULL value instead of an error when a conversion is impossible?
⚠ Common exam trap
Candidates rely on standard CAST() or TO_NUMBER() functions, which abort the entire query execution upon encountering unexpected non-numeric character strings.
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
✓
TRY_CAST()
Data quality issues are common during transformation. Standard casting functions like CAST() or TO_NUMBER() are strict and will terminate a query if they encounter invalid input. To build resilient pipelines, engineers use 'try' variants of these functions, which gracefully handle errors by returning a NULL, allowing the rest of the dataset to be processed without interruption.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
AS_INTEGER()
Why it's wrong here
AS_INTEGER is used for extracting integer values from VARIANT columns in semi-structured data. It is not a general-purpose casting function for string-to-number conversions. If used on a string that is not part of a variant object, it will not provide the error-handling behavior required to avoid query failure.
- ✗
TO_DECIMAL()
Why it's wrong here
TO_DECIMAL is a standard conversion function that is strict. If it encounters a string like 'ABC' while trying to convert to a number, it will throw an execution error and stop the query. It is suitable only when the data is guaranteed to be clean and conform to the target type.
- ✓
TRY_CAST()
Why this is correct
TRY_CAST is the safest choice for transformations where data quality is uncertain. It attempts to convert the value to the specified data type, but if the conversion fails, it returns NULL instead of raising an exception. This ensures that a few bad records do not crash an entire batch processing job.
- ✗
COALESCE()
Why it's wrong here
COALESCE is used to return the first non-null value from a list of arguments. While it is often used alongside conversion functions to provide a default value, it does not perform the conversion itself. It cannot prevent a casting error from occurring if the nested conversion function fails during execution.
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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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