SQL interview questions

SQL interviews are less about recalling every function and more about whether you can describe the rows you expect. Start there.

Name the grain

Before writing or describing a query, say what one row represents: an order, a customer-day, a ticket. Many wrong answers are correct-looking queries at the wrong grain.

Joins and filters

• Say which table you trust as the starting set.
• Say whether a join should keep unmatched rows, and why.
• Say which filter changes the business question, not only the row count.
• If you aggregate, say what you grouped by and what you deliberately did not group by.

Window functions

If you use a window function, say what the window is. “Rank of orders inside each customer” is a better sentence than the function name alone. If you have not used window functions at work, say that and explain the grouped query you would write instead.