Joins Interview Questions

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

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If we join two tables with an inner join, how many records will result? How many combinations will be produced?🟡 Medium · Conceptual · Asked 12×Which joins have you used?🟢 Easy · Conceptual · Asked 2×Given the EMPLOYEE table, write a query to retrieve each employee’s name along with their manager’s name.🟡 Medium · Coding · Asked 2×What is the difference between one-to-one and one-to-many relationships?🟢 Easy · Conceptual · Asked 2×For example, how can we use a CTE to simplify joins between tables?🟡 Medium · Conceptual · Asked 1×What is the difference between inner join and outer join?🟢 Easy · Conceptual · Asked 1×How many records are returned by the SQL join?🟢 Easy · Conceptual · Asked 1×Suppose you're given a dataset with 100 million rows and you need to perform a complex join operation between two tables. How would you optimize the join operation for better performance?🟡 Medium · Conceptual · Asked 1×Write an SQL query that displays each employee’s name along with their manager’s name using a self‑join on the Employee table.🟡 Medium · Coding · Asked 1×Write an SQL query that joins the Employee and Department tables to display employee name, department name, and salary, and then uses a window function to rank employees by salary within each department.🟡 Medium · Coding · Asked 1×Explain different types of joins in SQL.🟢 Easy · Conceptual · Asked 1×Given an orders table, an order_items table, and a products table, write a query to find products that were never sold.🟡 Medium · Coding · Asked 1×Write an SQL query to select the top 10 users by order count.🟢 Easy · Coding · Asked 1×Why can an INNER JOIN return fewer rows than either of the joined tables?🟢 Easy · Conceptual · Asked 1×Scenario: we have a massive sales table and a smaller product table. The join is taking too long. What would you do?🟡 Medium · Debugging · Asked 1×Explain the result of joining two tables: Table1 has one column with 3 records: 1, 1, NULL. Table2 has one column with 2 records: 1, NULL. What will be the result of a LEFT JOIN and an INNER JOIN?🟡 Medium · Conceptual · Asked 1×Explain joins in SQL.🟢 Easy · Conceptual · Asked 1×Can you tell me the types of joins in SQL?🟢 Easy · Conceptual · Asked 1×What would be the output of a left join? Suppose the master table is A and the other table is B. If we perform a left join, what would be the output?🟡 Medium · Conceptual · Asked 1×If you perform an inner join, many rows will become?🟢 Easy · Conceptual · Asked 1×In a query, many rows will come from which type of join?🟢 Easy · Conceptual · Asked 1×What are the types of joins? Write the output of each join.🟡 Medium · Conceptual · Asked 1×Given two tables A and B, can you write the number of rows that would result from an inner join, a left join, and an outer join?🟡 Medium · Conceptual · Asked 1×What are the types of joins in SQL?🟢 Easy · Conceptual · Asked 1×How can you resolve data skewing issues in Spark when performing joins?🟡 Medium · Conceptual · Asked 1×To contain all 10 teams, each must play every other team at home and away. Can you write a query to do this?🟡 Medium · Coding · Asked 1×Write an SQL query that returns the employee name and the manager name for each employee.🟢 Easy · Coding · Asked 1×Write an SQL query to count the number of employees reporting to each manager.🟡 Medium · Coding · Asked 1×Can you walk through a complex SQL query you have written recently in your career?🟡 Medium · Conceptual · Asked 1×List employees grouped by department who receive the second half of their salary.🟡 Medium · Coding · Asked 1×Suppose you have two tables, Employee and Department. Verbally explain how you would find the highest paid employee in each department.🟡 Medium · Coding · Asked 1×Can you explain a PySpark transformation you personally developed? What were the input DataFrames? What type of joins did you use? Did you save the input and output as views?🟡 Medium · Coding · Asked 1×What is the result of a join between table1 and table2?🟢 Easy · Conceptual · Asked 1×Explain how inner and left joins work in Python and provide examples.🟡 Medium · Conceptual · Asked 1×List the top 3 departments by revenue.🟡 Medium · Coding · Asked 1×He was asking about inner join, left join, right join, and full outer join. What will be the output of table A and table B?🟡 Medium · Conceptual · Asked 1×Given the following table schemas: TableA: id values 1, 1, 2, 3, 4 TableB: id values 1, 2, 2, 4 What are the results of an inner join, left join, right join, and full outer join on the id column?🟡 Medium · Conceptual · Asked 1×Given the following tables: TableA: | id | |----| | 1 | | 1 | | 2 | | 3 | | 4 | TableB: | id | |----| | 1 | | 2 | | 3 | | 4 | How many records would result from an inner join and from a left join on the id column?🟢 Easy · Conceptual · Asked 1×Can you tell the difference between an inner join and an outer join?🟢 Easy · Conceptual · Asked 1×What are the different types of joins in SQL?🟢 Easy · Conceptual · Asked 1×Do you know how to perform joins in SQL?🟢 Easy · Conceptual · Asked 1×In the last record I don't have an accepted date; how does an inner join work?🟡 Medium · Conceptual · Asked 1×In a SQL join, if we ignore the last record because it hasn't joined, will we get only three records for gate 4?🟡 Medium · Conceptual · Asked 1×If we have 3 accepted records and 4 sent records, and we perform an inner join between the sent and accepted tables, what will be the result?🟢 Easy · Conceptual · Asked 1×In a left join, does the join key matter? If the wrong join key is used, will it produce incorrect data?🟢 Easy · Conceptual · Asked 1×Why might a join fail when the data types of the join columns differ? The join key should match the current join key.🟡 Medium · Conceptual · Asked 1×Why am I using an inner join?🟢 Easy · Conceptual · Asked 1×Which key would you use to join tables?🟢 Easy · Conceptual · Asked 1×How do you perform an inner join on a key?🟢 Easy · Conceptual · Asked 1×What does an inner join return?🟢 Easy · Conceptual · Asked 1×Which join would you use to retrieve all records from one table and matching records from another?🟢 Easy · Conceptual · Asked 1×Explain the differences between inner, outer, left, and cross joins.🟢 Easy · Conceptual · Asked 1×When using an inner join, we get three successful counts instead of the total count. Will we then get the count?🟡 Medium · Conceptual · Asked 1×But in the last record I don't have a sent record or a reciprocal accepted record; how will an inner join work?🟡 Medium · Conceptual · Asked 1×Can you provide code that uses a left join?🟢 Easy · Coding · Asked 1×

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