Explain the difference between WHERE and HAVING clauses
This is a classic SQL question about filtering timing relative to aggregation. It tests logical flow understanding.
Why Interviewers Ask This
Interviewers want to see if you understand the order of operations in SQL execution. Confusing these leads to syntax errors and incorrect results. It proves you grasp when to filter raw data versus aggregated groups.
How to Answer This Question
Clarify that WHERE filters rows before grouping happens. State that HAVING filters groups after aggregation. Mention that WHERE cannot use aggregate functions, but HAVING can. Use a simple example to illustrate the difference.
Key Points to Cover
- WHERE filters before grouping
- HAVING filters after grouping
- WHERE excludes aggregates
- HAVING requires aggregates
Sample Answer
WHERE filters individual rows before any grouping or aggregation occurs, so it cannot use aggregate functions like SUM. It is best for narrowing down raw data early, such as filtering by date range. HAVING, however, filt…
Common Mistakes to Avoid
- Using aggregates in WHERE clause
- Confusing the execution order
- Thinking HAVING replaces WHERE entirely
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