Databricks-Spark-Assoc Using Spark SQL Practice Question
Which SQL function is used to concatenate strings while allowing you to specify a custom separator, handling null values by ignoring them?
⚠ Common exam trap
Many candidates confuse concat_ws() with standard concat(), overlooking how standard concat turns the entire output null if any single column contains a null value.
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
✓
concat_ws()
The 'concat_ws' function stands for 'concatenate with separator'. It is specifically designed to take a delimiter as the first argument, followed by a variable number of strings. A key feature of 'concat_ws' is its ability to skip NULL values automatically, preventing the entire result from becoming NULL—a common issue with the standard 'concat' function. This makes it ideal for building CSV-like strings or concatenating fields that may contain missing data.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
concat()
Why it's wrong here
The 'concat' function concatenates all provided arguments. However, if any of the input arguments are NULL, the result of the entire function is NULL. It also does not allow for a custom separator, forcing the user to add delimiters manually, which is inefficient for complex data structures.
- ✓
concat_ws()
Why this is correct
The 'concat_ws' function accepts a separator as its first argument and handles NULL values by ignoring them. This behavior is crucial for data cleaning and string formatting tasks where missing values should not invalidate the entire concatenated output, ensuring a consistent and readable result string for downstream consumers.
- ✗
array_join()
Why it's wrong here
While 'array_join' can combine elements of an array with a separator, it requires the input to be an array type. It is not designed to take multiple individual string columns as direct arguments. Converting columns to arrays just for concatenation is an unnecessary performance overhead for simple string operations.
- ✗
format_string()
Why it's wrong here
The 'format_string' function is used for printf-style formatting. While it can produce complex strings, it does not have the built-in capability to automatically skip NULL values or iterate over a variable number of arguments with a consistent separator without complex logic or nested ternary operators.
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Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Databricks exam blueprint
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