What is a Common Table Expression (CTE) and when do you use it?
This question tests your ability to write readable and modular SQL. It evaluates familiarity with temporary named result sets defined with the WITH clause.
Why Interviewers Ask This
Complex queries are hard to debug and maintain. CTEs help break down logic into manageable steps. Interviewers ask this to see if you prioritize code readability and modularity over writing monolithic subqueries.
How to Answer This Question
Define a CTE as a temporary named result set valid only for the current query. Explain its benefits: improved readability, easier debugging, and avoiding repeated subqueries. Mention recursive CTEs for hierarchical data like org charts.
Key Points to Cover
- CTEs are temporary named result sets
- Improve query readability
- Support recursive queries
Sample Answer
A CTE is a temporary result set defined with the WITH clause that exists only for the duration of a single statement. I use CTEs to break complex queries into logical steps, making the code much easier to read and debug.…
Common Mistakes to Avoid
- Treating CTEs as permanent tables
- Using them unnecessarily for simple queries
- Forgetting they are limited to one statement
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