SQL - LEFT and RIGHT JOIN
Find the problem in this query:
SELECT * FROM Products FULL OUTER JOIN Sales ON Products.id = Sales.product_id WHERE Sales.amount > 100;
Find the problem in this query: SELECT * FROM Products FULL OUTER JOIN Sales ON Products.id = Sales.product_id WHERE Sales.amount > 100;
medium📝 Debug Q7 of 15
Step-by-Step Solution
Solution:
Step 1: Understand FULL OUTER JOIN
It returns all rows from both tables, with NULLs where no match exists.Step 2: Analyze WHERE clause effect
WHERE Sales.amount > 100 excludes rows where Sales.amount is NULL, removing unmatched rows.Final Answer:
WHERE clause filters out NULLs, negating FULL OUTER JOIN effect -> Option AQuick Check:
WHERE filters can remove outer join unmatched rows [OK]
Quick Trick: Filter outer join results in ON, not WHERE, to keep NULLs [OK]
Common Mistakes:
MISTAKES- Filtering outer join results in WHERE clause
- Expecting NULLs to remain after WHERE filters
- Misunderstanding FULL OUTER JOIN behavior
Master "LEFT and RIGHT JOIN" in SQL
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