Joins
SQL Join Interview Questions
A join puts two tables side by side on a column they share, so you can use a name from one table and a number from the other. It is the most asked SQL topic in interviews, and the one that most often changes your row count without saying so.
What join questions ask you to do
Across the questions here, these are the shapes that come up:
- Bring in a name or label from a second table
- Find records that exist in one table and not the other
- Keep rows that have no match on the other side
- Compare a row with another row in the same table
- Match on a date range rather than on an exact value
Common mistakes with joins
A LEFT JOIN keeps rows that have no match on the other side, but adding a condition on that second table in the WHERE clause throws those same rows away again and quietly turns it back into an ordinary join. The other trap is joining on a column whose values repeat, which multiplies rows and inflates every total built on them.
Questions to practice
- Large orders with customer namesSQL
Amazoneasy - Watch time by genrePandas
Netflixeasy - Average rating by vehicle typePandas
Ubermedium - Average reactions per post typeSQL
Metamedium - Customers without ordersSQLAmazonmedium
- Drivers without ridesPandasUbermedium
- Employees and their managersSQL
Workdaymedium - Orders per customer segmentSQLAmazonmedium
- Prime vs. standard order valueSQLAmazonmedium
- Revenue by countrySQL
Stripemedium - Revenue by statePandasAmazonmedium
- Subtasks that outlived the parentSQLPremium
Atlassianmedium - Verified rating by shopSQL
Etsymedium - Incidents that overlappedSQL
Datadoghard - Top spending customersSQLAmazonhard
Questions last reviewed 19 October 2026.