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What is a semi-join?

SQLmedium0.6 min readPremium
Frequency
Low
Asked at 1 company
Category
487
questions in SQL
Difficulty Split
130E|271M|86H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Altimetrik
Key Concepts Tested
join
Expert AnswerPremium
118 wordsInterview-ready
Semi-join returns rows from the left table that have at least one match in the right table, but doesn't duplicate left rows. Implementation: SELECT * FROM a WHERE EXISTS (SELECT 1 FROM b WHERE b.id = a.id) or IN. Unlike inner join, semi-join returns one row per left match even if multiple right matches exist. Use cases: Filter to customers who have orders; exclude/include based on existence....
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