Data interviews test SQL in predictable ways. The questions return to joins, grouping with aggregation, filtering aggregated results, and window functions for ranking and running totals. Candidates who practise these patterns on real tables answer calmly. Candidates who only read about them freeze when the query gets nested.
Drills that build fluency
- Join two tables and explain each row of the result, since misunderstanding joins causes most SQL errors.
- Practise grouping with conditions on the group, which is where beginners confuse row filters and group filters.
- Learn one window function well, such as ranking within groups, before collecting several you cannot use.
- Work with messy sample data, including duplicates and missing values, because interview data is rarely clean.
During the interview, talk through your query before writing it. Interviewers credit clear reasoning even when the final syntax needs a fix.