SQL Basics
What does SELECT do in SQL?
It retrieves data from a table.
What is a “missing value”?
Data that wasn’t recorded or is blank/NULL.
What is a “dimension” in Tableau?
Categorical field used for slicing data.
What does the “mean” measure?
The average value.
What is a requirement?
A need or condition to meet for a solution.
What SQL keyword removes duplicates?
DISTINCT
What is normalization?
Standardizing or scaling data to a similar range.
What is a “measure”?
Numeric field used for aggregation.
What is correlation?
Strength/direction of relationship between two variables.
What is a KPI?
A measurable value that indicates performance.
Which clause filters results after grouping?
HAVING
Name two ways to handle outliers.
Remove, cap (winsorize), transform, investigate source.
Which chart type is best for showing trends over time?
Line chart.
What is standard deviation?
How spread out values are from the mean.
Define “stakeholder.”
Anyone affected by or involved in a project.
Name one type of SQL JOIN.
INNER, LEFT, RIGHT, FULL OUTER
What is data type coercion?
Converting data types (e.g., text → number).
What is a calculated field?
A user-created field using formulas.
What is a p-value?
Probability of getting results if the null hypothesis is true.
What are functional vs. non-functional requirements?
Functional: What the system does
Non-functional: How the system behaves (quality, speed)
What’s the main difference between WHERE and HAVING?
WHERE filters rows before grouping
HAVING filters groups after grouping
What is the difference between wide and long data?
Wide: Each variable has its own column
Long: Variables are stacked in rows with identifiers
What is the difference between blending and joining?
Join: Combines tables at the row level
Blend: Combines after aggregation, keeping sources separate
Explain the Central Limit Theorem.
Large samples → sampling distribution becomes normal regardless of original distribution.
What is a use case?
A scenario showing how a user interacts with a system.