What does COALESCE do in SQL?
It returns the first non-null expression. Use it to supply a fallback when a missing value has a defined replacement.
How do I find customers with no orders in SQL?
Use NOT EXISTS with a matching customer ID, or a LEFT JOIN followed by a check for a missing order key.
What is the difference between RANK and ROW_NUMBER in SQL?
ROW_NUMBER assigns a different number to each row. RANK gives tied rows the same rank and leaves gaps after a tie.
Why is my percentage total wrong in a dashboard?
Averaging row percentages can give the wrong result when denominators differ. Calculate the overall numerator divided by the overall denominator.
How can I check whether data loaded completely?
Compare row counts, date ranges and control totals with the source. Break the checks down by date or batch to locate missing records.
When should I use a bar chart instead of a pie chart?
Use bars when readers need to compare similar values or many categories. A shared baseline makes differences easier to see.
What is a cohort in analytics?
It is a group defined by a shared starting event or characteristic, such as customers who first purchased in June.
How do I explain a month with incomplete sales data?
Label it as partial and state the cutoff date. Compare it with the equivalent portion of a prior period if that comparison fits the question.
Explore related topics in the ScholarLogic project Q&A guide.
