What is Join and what are its types in SQL?
Tests understanding of combining rows from two or more tables based on related columns.
Why Interviewers Ask This
Joins are fundamental for querying relational data. Interviewers assess your ability to retrieve complex data sets and understand inner vs outer joins.
How to Answer This Question
Define a join as combining rows from tables. List types: Inner, Left, Right, Full, and Cross joins. Explain the result set for each. Provide examples of when to use specific join types based on data requirements.
Key Points to Cover
- Definition of join
- Inner vs Outer joins
- Result set behavior
- Use cases
Sample Answer
A join combines rows from two or more tables based on a related column. Inner joins return matching records, while Left joins keep all left records even if no match exists. Right and Full joins handle similar scenarios for the opposite or both sides. Choosing the right join is critical for accurate data retrieval.
Common Mistakes to Avoid
- Confusing inner and outer joins
- Ignoring NULL handling
- Forgetting cross joins
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