Module 08: Debugging, Assignments, Glossary & 50+ Interview Q&A Bank

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Common DAX Errors & Troubleshooting Table

Problem / Error	Possible Cause	Fix / Solution
Single value cannot be determined	Passing a column to measure without aggregation	Wrap column in SUM(), MAX(), or SELECTEDVALUE()
Incorrect totals in visual	Measure ignoring table grain or filter context	Use SUMX() or adjust CALCULATE filter modifiers
Blank result	Date table disconnect or missing filter match	Check relationships & date table coverage
Divide by zero error	Standard division `/` by 0	Use `DIVIDE(num, denom, 0)`
Month names out of order	Alphabetical sorting default	Sort Month Name column by Month Number
Percentage 100x too high	Multiplied formula by 100 while applying % format	Remove `* 100` from formula
Previous year blank	Missing prior year dates in Date table	Expand CALENDAR date range
Circular dependency	Calculated columns referencing each other	Refactor to measures or review model design

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12 Practice Assignments with Hints & Formulas

No.	Task / Assignment	Hint / Formula
1	Total sales	SUM(Sales[Sales])
2	Total cost	SUM(Sales[Cost])
3	Total profit	[Total Sales] - [Total Cost]
4	Profit margin	DIVIDE([Total Profit], [Total Sales], 0)
5	Label sales >= 50000 as High	IF(Sales[Sales] >= 50000, "High", "Low")
6	Mohali sales	CALCULATE([Total Sales], Sales[City] = "Mohali")
7	Unique cities count	DISTINCTCOUNT(Sales[City])
8	Count total rows	COUNTROWS(Sales)
9	Sum sales > 10000 rows	CALCULATE([Total Sales], FILTER(Sales, Sales[Sales] > 10000))
10	Top 5 products	RANKX or visual Top N filter
11	Previous month sales	PREVIOUSMONTH + CALCULATE
12	Running total	CALCULATE + FILTER + ALLSELECTED

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50+ Power BI & DAX Master Interview Q&A

❓ Core Concept Interview Q&A

Q: What is the difference between Power Query and DAX? Power Query is an ETL tool used for data cleaning and transformation before loading into the model; DAX is a calculation engine used for dynamic reporting, measures, and business analytics.

Q: Difference between Calculated Column and Measure? A column calculates values row-by-row at refresh time and stores them in RAM; a measure calculates on-the-fly inside the active visual filter context.

Q: How does CALCULATE work? `CALCULATE` evaluates an expression in a modified filter context by adding, removing, or updating active table filters.

Q: What is Context Transition? Context Transition occurs when `CALCULATE()` is invoked inside a row context (like SUMX or a Calculated Column), converting the current row into an equivalent filter context.