SQL Join Interview Questions

Write an INNER JOIN Query

Write a SQL query to find all employees and their department names using INNER JOIN.

Expected output: List of employees with their corresponding department names.

Hint: Join Employees and Departments tables on DepartmentID.

Use LEFT JOIN to Find Missing Data

Write a query to list all products and their sales, including products with no sales.

Expected output: All products listed with sales data or NULL if no sales.

Hint: Use LEFT JOIN between Products and Sales tables.

INNER JOIN returns only rows with matching values in both tables, while LEFT JOIN returns all rows from the left table and matched rows from the right table, including unmatched rows with NULLs.

CROSS JOIN is used to produce a Cartesian product of two tables, useful for generating combinations or testing, but rarely used in production queries.

FULL OUTER JOIN returns all rows from both tables, matching where possible and filling with NULLs where there is no match, unlike LEFT or RIGHT JOIN which return all rows from only one table.