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SQL Query: 3 Methods for Calculating Cumulative SUM

SQL provides various constructs for calculating cumulative sums, offering flexibility and efficiency in data analysis. In this article, we explore three distinct SQL queries that facilitate the computation of cumulative sums. Each query leverages different SQL constructs to achieve the desired outcome, catering to diverse analytical needs and preferences. Using Window Functions (e.g., PostgreSQL, SQL Server, Oracle) SELECT id, value, SUM(value) OVER (ORDER BY id) AS cumulative_sum  FROM your_table; This query uses the SUM() window function with the OVER clause to calculate the cumulative sum of the value column ordered by the id column. Using Subqueries (e.g., MySQL, SQLite): SELECT t1.id, t1.value, SUM(t2.value) AS cumulative_sum FROM your_table t1 JOIN your_table t2 ON t1.id >= t2.id GROUP BY t1.id, t1.value ORDER BY t1.id; This query uses a self-join to calculate the cumulative sum. It joins the table with itself, matching rows where the id in the first table is greater than or

15 Top Data Analyst Interview Questions: Read Now

We will explore the world of data analysis using Python, covering topics such as data manipulation, visualization, machine learning, and more. Whether you are a beginner or an experienced data professional, join us on this journey as we dive into the exciting realm of Python analytics and unlock the power of data-driven insights. Let's harness Python's versatility and explore the endless possibilities it offers for extracting valuable information from datasets. Get ready to level up your data analysis skills and stay tuned for informative and practical content!

Data Analyst Interview Questions

Python Data Analyst Interview Questions

01: How do you import the pandas library in Python? 

A: To import the pandas library in Python, you can use the following statement: import pandas as pd.

Q2: What is the difference between a Series and a DataFrame in pandas? 

A: A Series in pandas is a one-dimensional labeled array, while a DataFrame is a two-dimensional labeled data structure with columns of potentially different types.

Q3: How do you read a CSV file into a DataFrame using pandas? 

A: To read a CSV file into a DataFrame using pandas, you can use the read_csv() function. For example: df = pd.read_csv('filename.csv').

Q4: What is the purpose of the NumPy library in Python analytics? 

A: The NumPy library in Python analytics is used for numerical computing. It provides mathematical functions and tools for working with multidimensional arrays, which are used by other libraries like pandas and scikit-learn.

Q5: How do you perform data cleaning and preprocessing using pandas? 

A: Data cleaning and preprocessing using pandas can involve tasks such as handling missing values, removing duplicates, transforming data types, and normalizing data.

Q6: How do you calculate descriptive statistics (mean, median, etc.) using pandas? 

A: To calculate descriptive statistics using pandas, you can use functions like mean(), median(), std(), min(), max(), and describe().

Q7: How do you handle missing values in a DataFrame? 

A: In pandas, missing values can be handled using functions like isnull(), fillna(), and dropna().

Q8: How do you merge/join multiple DataFrames in pandas? 

A: To merge/join multiple DataFrames in pandas, you can use functions like concat(), merge(), and join().

Q9: How do you perform groupby operations and aggregations in pandas? 

A: Groupby operations and aggregations in pandas can be performed using the groupby() function.

Q10: How do you visualize data using matplotlib or seaborn libraries in Python? 

A: Data visualization in Python can be done using libraries like matplotlib and seaborn.

Q11: What is the purpose of the scikit-learn library in Python analytics? 

A: The scikit-learn library in Python analytics is used for machine learning tasks.

Q12: How do you split data into training and testing sets using scikit-learn? 

A: To split data into training and testing sets using scikit-learn, you can use the train_test_split() function.

Q13: How do you perform feature scaling in scikit-learn? 

A: Feature scaling in scikit-learn is important to ensure that all features have a similar scale.

Q14: What are some commonly used machine learning algorithms in scikit-learn? 

A: Scikit-learn provides a wide range of machine learning algorithms, including linear regression, logistic regression, decision trees, random forests, support vector machines, k-nearest neighbors, and neural networks.

Q15: How do you evaluate the performance of a machine learning model using metrics like accuracy, precision, and recall? 

A: The performance of a machine learning model can be evaluated using metrics like accuracy, precision, recall, and F1 score.


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