PL-300 Model the data Practice Question
Your Power BI model includes a calculated column that concatenates first and last name. Users report that the column shows blank for some rows. The data source has no nulls. What is the most likely cause?
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
✓
One of the columns contains only spaces
A column containing only spaces (e.g., ' ') is not null, but when concatenated with another name, the result may appear blank if the concatenation results in pure whitespace or if the column is trimmed before concatenation. Option A is incorrect because data type mismatch would typically cause an error, not a blank result. Option B is incorrect because the data source has no nulls, so missing rows are not the issue. Option C is incorrect because relationship direction does not affect calculated columns within the same table.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Data type mismatch between the two columns
Why it's wrong here
A data type mismatch between the two columns would not produce blank results because the DAX concatenation operator `&` explicitly coerces both operands to text before combining them. For example, concatenating a numeric 123 with a text "ABC" yields "123ABC", not a blank. If the conversion is impossible, DAX returns a conversion error, such as with binary data, not an empty string.
- ✗
The columns are from different tables without a relationship
Why it's wrong here
If the two columns exist in different tables and have no active relationship, the calculated column formula will fail to compile because DAX cannot resolve an unqualified column reference outside the current table. Calculated columns operate within row context of the base table, and referencing a column from an unrelated table requires `RELATED` or `LOOKUPVALUE` with a defined relationship. This would raise an error, not silently yield blank values.
- ✗
The relationship between tables is set to single direction
Why it's wrong here
Relationship direction, whether single or bidirectional, controls filter propagation in measures and visuals, not how a calculated column evaluates row-by-row at refresh time. A calculated column can use `RELATED` to pull a value from a related table along any relationship whose direction permits from the current table to the target — for single-direction, this always works from many side to one side. Therefore, setting the relationship to single direction would not cause blank results in the concatenated calculated column.
- ✓
One of the columns contains only spaces
Why this is correct
If one column contains only spaces (for example, a person's last name field holding `" "`), the concatenated result is a string composed entirely of whitespace. Because DAX does not automatically trim leading or trailing spaces in concatenation, the resulting column looks empty in visuals and may be treated as blank by later functions, even though it is not a true BLANK. This explains why the calculated column appears blank while actually holding a space-only value.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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