Level up your career with comprehensive practice exams covering SQL, Python, Statistics, and Visualization.

Data Analyst Interview Practice Questions and Answers with detailed explanations are designed to help you bridge the gap between theoretical knowledge and real-world analytical execution. I have meticulously crafted this course to cover every essential pillar of the field, from statistical thinking and complex SQL window functions to Python automation and business storytelling. Whether you are preparing for a high-stakes technical interview or a professional certification, I provide deep-dive insights into exploratory data analysis (EDA), hypothesis testing, and dashboard best practices that modern employers demand. By practicing with these realistic scenarios, you will not only learn how to identify the correct answer but also understand the underlying logic required to solve complex data problems and communicate findings effectively to stakeholders.

Exam Domains & Sample Topics

Data Analysis Fundamentals: Descriptive/Inferential Statistics, Probability, and Hypothesis Testing.
SQL & Data Wrangling: Joins, Aggregations, Window Functions, and Data Cleaning logic.
Visualization & Storytelling: Power BI/Tableau best practices, Chart Selection, and KPI Design.
Python/R & Tooling: Pandas, NumPy, Scripting, Automation, and API integration.
Advanced Analytics: A/B Testing, Forecasting, Data Ethics, and Performance Optimization.

Sample Practice Questions

Question 1: Which of the following SQL clauses is processed FIRST by the database engine during execution?
- A) SELECT
- B) WHERE
- C) FROM
- D) GROUP BY
- E) HAVING
- F) ORDER BY
- Correct Answer: C
- Overall Explanation: SQL queries follow a specific logical processing order that differs from how the code is written.
- Detail Explanation:
  - A) Incorrect: SELECT is processed late, after filtering and grouping.
  - B) Incorrect: WHERE happens after the data source is identified.
  - C) Correct: The engine must first identify the table (FROM) before any other operation.
  - D) Incorrect: Grouping occurs after filtering with WHERE.
  - E) Incorrect: HAVING filters groups after they are created.
  - F) Incorrect: ORDER BY is almost always the final step for sorting the final output.
Question 2: In a normal distribution, what percentage of data falls within two standard deviations (±2σ) of the mean?
- A) 50%
- B) 68%
- C) 90%
- D) 95%
- E) 99.7%
- F) 100%
- Correct Answer: D
- Overall Explanation: The Empirical Rule (68-95-99.7) defines the spread of data in a Gaussian distribution.
- Detail Explanation:
  - A) Incorrect: 50% represents data on either side of the mean.
  - B) Incorrect: 68% falls within one standard deviation.
  - C) Incorrect: 90% is a common confidence interval but not a standard deviation marker.
  - D) Correct: Approximately 95% of observations fall within two standard deviations.
  - E) Incorrect: 99.7% falls within three standard deviations.
  - F) Incorrect: The tails of a normal distribution are asymptotic and never reach 100%.
Question 3: You are using Python's Pandas library. Which method is most efficient for handling missing values by replacing them with the mean of the column?
- A) df.dropna()
- B) df.describe()
- C) df.fillna()
- D) df.replace()
- E) df.isna()
- F) df.pivot()
- Correct Answer: C
- Overall Explanation: Data imputation is a core part of the wrangling process to maintain dataset integrity.
- Detail Explanation:
  - A) Incorrect: dropna() removes the rows/columns entirely.
  - B) Incorrect: describe() provides summary statistics but doesn't modify data.
  - C) Correct: fillna() is specifically designed to populate null values with a specific value or logic.
  - D) Incorrect: replace() is used for general value swapping, not specifically optimized for Nulls.
  - E) Incorrect: isna() only detects missing values; it does not fix them.
  - F) Incorrect: pivot() reshapes the data structure.

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