DP-203 Case sensitivity in mapping data flows Practice Question
You are developing a data processing pipeline in Azure Synapse Analytics. The pipeline uses a mapping data flow to transform data from Azure Data Lake Storage Gen2 to a dedicated SQL pool. The data flow includes a Derived Column transformation that uses the expression: `iif(isnull(Column1), 'Default', Column1)`. However, the transformation is not handling NULL values correctly. What is the most likely cause?
⚠ Common exam trap
Candidates often assume function names in Azure Synapse mapping data flows are case-insensitive like in SQL, but they are actually case-sensitive, causing a seemingly correct expression to fail due to a subtle casing error.
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
✓
The function names in the expression are case-sensitive; use 'isNull' instead of 'isnull'.
The function names in Azure Synapse mapping data flows are case-sensitive. The expression uses `isnull` (all lowercase), but the correct function name is `isNull` (capital 'N'). When the function name is typed with incorrect casing, the Derived Column transformation fails to recognize the function and does not evaluate the null check correctly, leading to NULL values not being replaced with 'Default'.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The Derived Column transformation does not support the iif function; use a Conditional Split instead.
Why it's wrong here
This is incorrect. The Derived Column transformation does support the `iif` function; a Conditional Split is used for routing data based on conditions, not for replacing nulls.
- ✗
The column data type is not string; convert Column1 to string first.
Why it's wrong here
This is incorrect. While data type conversion might be needed in some cases, the `iif` function can handle non-string types. The most likely cause here is the casing of the function name, not the data type.
- ✓
The function names in the expression are case-sensitive; use 'isNull' instead of 'isnull'.
Why this is correct
This is correct. The function names are case-sensitive; the expression uses `isnull` (all lowercase), but the correct function name is `isNull` with a capital 'N'. This causes the transformation to fail to interpret the function correctly.
- ✗
The expression must use ternary operator syntax: `Column1 == null ? 'Default' : Column1`.
Why it's wrong here
This is incorrect. Mapping data flows do not support the ternary operator syntax (`? :`); the `iif` function is the correct syntax for conditional logic.
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