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Count records for INNER JOIN and LEFT JOIN

SQLmedium0.5 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
Pubmatic
Key Concepts Tested
join
Expert AnswerPremium
98 wordsInterview-ready
**Architectural Logic**: Join type determines output cardinality and null semantics. **INNER JOIN**: Only matching rows from both tables; count ≤ min(left, right) when 1:1 or N:1. **LEFT JOIN**: All left rows; right columns NULL where no match; count = left count (if left is 'one' side). **Cardinality Rules**: INNER can reduce rows (excludes orphans); LEFT preserves left. Use COUNT(*) for total rows; COUNT(right.key) for non-null matches (LEFT JOIN gives matched count)....
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