Joins Interview Questions

20 real Joins questions asked in live technical interviews — each with a model answer. Updated weekly.

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What is question 2 in PySpark?🟡 Medium · Conceptual · Asked 2×What are some join strategies in Spark, and when is each best used?🟡 Medium · Conceptual · Asked 2×Given a dataset of employees and managers, write a query to fetch all employees who earn more than their managers.🟡 Medium · Conceptual · Asked 1×Complete the SQL query by adding the missing FROM and JOIN clauses to join on empid.🟢 Easy · Coding · Asked 1×Can you explain how joins work in Spark?🟡 Medium · Conceptual · Asked 1×What is the difference between an anti join and a left anti join?🟡 Medium · Conceptual · Asked 1×What is the difference between a left join and a right join?🟢 Easy · Conceptual · Asked 1×How would you optimize a SQL query in Snowflake that involves multiple joins?🟡 Medium · Conceptual · Asked 1×Give me a brief on how a SQL join works.🟢 Easy · Conceptual · Asked 1×Suppose you have a join where one customer ID accounts for about 40% of the entire dataset. What problems can arise from this skew?🟡 Medium · Conceptual · Asked 1×How do you perform a full outer join on `txn_id` and flag rows where either side is missing?🟡 Medium · Conceptual · Asked 1×What are the SQL queries to answer the following three questions: (1) Retrieve employee and manager names, showing 'TBO' if no manager; (2) List employees earning more than the average salary; (3) Get manager level and total salary for their hierarchy.🟡 Medium · Coding · Asked 1×What are the SQL queries to answer the following three questions: (1) Retrieve manager name, or 'TBD' if missing; (2) List employees earning more than the average salary; (3) Get manager name and total salary of their hierarchy, including the manager, but only if the total exceeds 100k.🟡 Medium · Coding · Asked 1×What are the SQL queries to answer the following three questions: (1) Retrieve employee and manager names, showing 'TBO' if no manager; (2) List employees earning more than the average salary; (3) Get manager salary at their level and total salary of their hierarchy.🟡 Medium · Coding · Asked 1×How would you join these two tables, and what would the resulting dataset contain?🟡 Medium · Conceptual · Asked 1×How would you perform a join between these two tables using the primary key and foreign key columns?🟡 Medium · Conceptual · Asked 1×How would you join the customer and orders tables using the customer ID, and what information would you retrieve?🟡 Medium · Conceptual · Asked 1×What is a source‑target join, and how would you implement it?🟡 Medium · Conceptual · Asked 1×Which type of join will you use?🟢 Easy · Conceptual · Asked 1×Given the table of user interactions with actions 'sent' and 'accepted', how would you find pairs of users who have not performed both actions on the same day?🟡 Medium · Coding · Asked 1×

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