PL-300 Model the data Practice Question
You need to create a calculated column in Power BI that shows the full name by combining 'FirstName' and 'LastName' columns with a space. Which DAX expression should you use?
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
✓
FullName = [FirstName] & " " & [LastName]
The DAX concatenation operator is the ampersand (&). Option B is wrong because CONCATENATE function only takes two arguments. Option C is wrong because CONCATENATEX is for tables. Option D is wrong because the plus sign is for addition.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
FullName = [FirstName] & " " & [LastName]
Why this is correct
The ampersand (&) is DAX's dedicated string concatenation operator, correctly joining the [FirstName] and [LastName] column values together with a literal space in between. It performs implicit data-type conversion when needed, so even if one column is stored as text and the other as a number, the result is a single text string. This syntax is the standard, efficient, and readable way to build a calculated column in Power BI.
- ✗
FullName = CONCATENATE([FirstName], " ", [LastName])
Why it's wrong here
The CONCATENATE function in DAX accepts exactly two arguments, so passing the space as a third argument here causes a syntax error. To join three or more values, you must either nest CONCATENATE calls or switch to the ampersand operator, which handles any number of operands. Thus, this expression is invalid as written and cannot be used to create the calculated column.
- ✗
FullName = CONCATENATEX(Table, [FirstName] & " " & [LastName])
Why it's wrong here
CONCATENATEX is an iterator function designed to evaluate an expression across all rows of a table and then concatenate the resulting values into one aggregate string, optionally using a delimiter. In a calculated column, you need a row-level result, not an aggregated single string across the entire table; this expression would attempt to concatenate every first/last name pair in the table into one huge value, and it is also missing the required delimiter argument. It is the wrong tool for this row-by-row operation.
- ✗
FullName = [FirstName] + " " + [LastName]
Why it's wrong here
The plus sign (+) in DAX is the arithmetic addition operator, not a string concatenation operator. When applied to text values, it attempts numeric coercion, which typically fails and raises an error because strings like names cannot be implicitly converted to numbers. Unlike the ampersand, the plus sign serves no purpose in building a full-name text string.
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