COUNT(column) vs COUNT(*) in SQL — With INNER, LEFT, RIGHT & FULL JOIN Explained
📰 Dev.to · Tim Nguyen
Learn the difference between COUNT(column) and COUNT(*) in SQL when using INNER, LEFT, RIGHT, and FULL JOIN to avoid common bugs
Action Steps
- Use COUNT(column) to count non-NULL values in a specific column
- Use COUNT(*) to count all rows in a result set, including NULL values
- Apply INNER JOIN to count matching rows between two tables
- Apply LEFT JOIN to count all rows from the left table and matching rows from the right table
- Apply RIGHT JOIN and FULL JOIN to understand how COUNT(column) and COUNT(*) behave with different join types
Who Needs to Know This
Database administrators, data analysts, and backend developers can benefit from understanding the nuances of COUNT(column) and COUNT(*) in SQL joins to write more accurate queries
Key Insight
💡 COUNT(column) only counts non-NULL values, while COUNT(*) counts all rows, including NULL values
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📊 COUNT(column) vs COUNT(*) in SQL: know the difference to avoid bugs in your joins!
Full Article
Counting seems simple in SQL… until joins enter the picture. One of the most common bugs...
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