What is Join and explain its types?
This SQL question covers joining tables, a fundamental operation. It tests query construction skills.
Why Interviewers Ask This
Joins are essential for retrieving related data. Interviewers assess your ability to combine datasets efficiently. Mastery here is required for reporting and analytics.
How to Answer This Question
Define JOIN as combining rows from two tables based on a related column. List types: INNER, LEFT, RIGHT, FULL OUTER. Explain output differences for each. Mention self-joins and cross joins. Provide simple examples.
Key Points to Cover
- Join definition
- INNER vs OUTER
- Left/Right specifics
- Matching logic
Sample Answer
A JOIN combines rows from two or more tables based on a related column between them. INNER JOIN returns only matching rows. LEFT JOIN returns all left rows and matches from the right. RIGHT JOIN does the opposite. FULL OUTER JOIN returns all rows when there is a match in either table. Understanding these types is crucial for accurate data retrieval in complex queries.
Common Mistakes to Avoid
- Confusing inner and outer
- Ignoring NULL handling
- No type list
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