In today’s data-driven world, organizations like PTC Company rely heavily on data science and analytics professionals to derive meaningful insights from data. Whether you’re a seasoned data scientist or a fresh graduate entering the field, preparing for a data science interview at PTC Company requires a solid understanding of key concepts and the ability to articulate your skills effectively. In this blog, we’ll explore some common data science and analytics interview questions along with their answers, tailored specifically for aspiring candidates at PTC Company.
Table of Contents
SQL and SQL joins Interview Questions
Question: What are the different types of SQL joins?
Answer: There are four main types of SQL joins:
- INNER JOIN: Returns records that have matching values in both tables.
- LEFT JOIN (or LEFT OUTER JOIN): Returns all records from the left table, and the matched records from the right table. If there are no matches, NULL values are returned for the columns from the right table.
- RIGHT JOIN (or RIGHT OUTER JOIN): Returns all records from the right table, and the matched records from the left table. If there are no matches, NULL values are returned for the columns from the left table.
- FULL JOIN (or FULL OUTER JOIN): Returns all records when there is a match in either left or right table. If there is no match, NULL values are returned for the missing side.
Question: Explain the difference between INNER JOIN and OUTER JOIN.
Answer:
- INNER JOIN: Retrieves records that have matching values in both tables being joined. It returns only the rows for which there is at least one match in both tables.
- OUTER JOIN: Retrieves all the rows from one table, even if there are no matches in the other table. It includes rows from one table that do not have corresponding rows in the other table, and vice versa.
Question: What is a primary key and foreign key in SQL?
Answer:
- Primary Key: A primary key is a unique identifier for each record in a table. It ensures that each row in a table is uniquely identifiable. Primary keys are defined when creating a table and are used to enforce entity integrity.
- Foreign Key: A foreign key is a field in a table that is a primary key in another table. It establishes a link between two tables by referencing the primary key of one table in the other table. Foreign keys are used to enforce referential integrity.
Question: How do you optimize SQL queries for better performance?
Answer: Use indexes appropriately on columns frequently used in WHERE, JOIN, and ORDER BY clauses.
- Minimize the use of functions in WHERE clauses as it can prevent the use of indexes.
- Use appropriate join types based on the relationship between tables.
- Avoid using SELECT * and instead specify only the columns needed.
- Use EXISTS or IN instead of DISTINCT when possible.
- Regularly analyze and optimize query execution plans.
- Properly normalize the database schema to reduce redundancy and improve query performance.
Question: Explain the difference between UNION and UNION ALL.
Answer:
- UNION: Combines the results of two or more SELECT statements into a single result set and removes duplicate rows from the result set.
- UNION ALL: Combines the results of two or more SELECT statements into a single result set without removing duplicate rows. It includes all rows from all SELECT statements, even if there are duplicates.
Question: What is a self-join?
Answer: A self-join is a join operation in which a table is joined with itself. It is used to combine rows with other rows in the same table based on a related column. Self-joins are often used when a table contains hierarchical data or when comparing rows within the same table.
Question: What is the difference between a subquery and a join?
Answer:
- Subquery: A subquery is a query nested inside another query. It is enclosed within parentheses and is executed before the main query. Subqueries can be used to return a single value, a list of values, or a result set that is used by the outer query.
- Join: A join is used to combine rows from two or more tables based on a related column between them. It is used to retrieve data from multiple tables simultaneously based on a related column or columns.
Question: How do you perform a cross join in SQL?
Answer: A cross join (or Cartesian join) is performed by simply listing the tables involved in the FROM clause with no joining condition. It returns the Cartesian product of the two tables, meaning each row from the first table is combined with every row from the second table.
Window Function Interview Questions
Question: Explain the difference between aggregate functions and window functions.
Answer:
- Aggregate functions: Aggregate functions operate on a set of rows and return a single value for each group of rows. They require a GROUP BY clause to partition the rows into groups.
- Window functions: Window functions perform calculations across a set of rows related to the current row, without collapsing the result set into a single row. They do not require a GROUP BY clause and can be used to perform calculations over a sliding window of rows.
Question: How do you define a window in a window function?
Answer: A window in a window function is defined using the OVER clause. It specifies the window of rows over which the function will operate. The window can be defined based on criteria such as partitioning, ordering, and framing.
Question: How do you partition rows in a window function?
Answer: Rows can be partitioned in a window function by specifying the PARTITION BY clause within the OVER clause. This partitions the result set into groups of rows based on the values of one or more columns. The window function is then applied independently to each partition.
Question: Explain the concept of window framing in window functions.
Answer: Window framing defines the subset of rows within the partition over which the window function operates. It is specified using the ROWS or RANGE clause within the OVER clause. ROWS framing defines a fixed number of rows relative to the current row, while RANGE framing defines a variable range of rows based on their values.
Question: What is the difference between ROWS and RANGE framing in window functions?
Answer:
- ROWS framing: Specifies a fixed number of rows relative to the current row as the window frame. It is not affected by the values of the rows, only their positions within the partition.
- RANGE framing: Specifies a variable range of rows based on their values relative to the current row. It considers the actual values of the rows and includes rows with equal values in the frame.
Question: How do you handle ties in window functions?
Answer: Ties in window functions can be handled using appropriate ranking functions such as RANK() or DENSE_RANK(). These functions assign unique ranks to each row within a partition, handling ties by assigning the same rank to rows with equal values.
Power BI Interview Questions
Question: Can you explain the difference between calculated columns and measures in Power BI?
Answer:
- Calculated columns: These are static values computed row by row within a table using DAX expressions. They are typically used for creating new columns based on existing data.
- Measures: These are dynamic aggregations or calculations that are evaluated based on the context of the visualization or user interaction. Measures are commonly used for calculations like sum, average, or count across multiple rows or tables.
Question: How do you create relationships between tables in Power BI?
Answer: Relationships between tables in Power BI can be established by matching columns with related data. This is done using the Manage Relationships feature in Power BI Desktop, where users define the relationships based on common fields with similar data types.
Question: What is a Power BI dashboard, and how do you create one?
Answer: A Power BI dashboard is a single-page canvas that displays key insights and visualizations from multiple reports or datasets. Users can create a dashboard in Power BI by pinning visuals from different reports or datasets to a dashboard canvas, arranging them, and adding text boxes or images for additional context.
Question: How do you share Power BI reports and dashboards with others?
Answer: Power BI reports and dashboards can be shared with others by publishing them to the Power BI service or to a workspace within Power BI online. Users can then share the reports with specific individuals or groups by granting them access permissions or by embedding the reports in web pages or applications.
Question: What are Power BI gateways, and why are they important?
Answer: Power BI gateways are software components that enable Power BI to connect securely to on-premises data sources. They are important because they allow users to refresh data in Power BI reports and dashboards from on-premises databases or data sources, ensuring that the reports are updated with the latest data.
Question: How do you schedule data refresh in Power BI?
Answer: Data refresh in Power BI can be scheduled using the Power BI service by configuring a refresh schedule for datasets. Users can specify the frequency and time for data refresh, along with credentials for accessing the data sources, ensuring that reports and dashboards are updated with the latest data automatically.
Question: Explain the difference between Power BI Desktop and Power BI Service.
Answer:
- Power BI Desktop: This is a desktop application used to create and author reports and dashboards locally on a user’s computer.
- Power BI Service: Also known as Power BI online, it is a cloud-based platform for publishing, sharing, and collaborating on Power BI content, including reports, dashboards, and datasets.
Conclusion
Preparing for a data science and analytics interview at PTC Company requires a deep understanding of fundamental concepts, hands-on experience with data analysis tools and techniques, and the ability to communicate technical concepts effectively. By familiarizing yourself with these common interview questions and their answers, you’ll be better equipped to showcase your skills and expertise in the field of data science, ultimately increasing your chances of success in landing your dream job at PTC Company.
