SQL - Advanced Query Patterns
Given the table employees with columns id and email, what will this query return?
SELECT email FROM employees GROUP BY email HAVING COUNT(*) > 1;
Given the table employees with columns id and email, what will this query return? SELECT email FROM employees GROUP BY email HAVING COUNT(*) > 1;
medium📝 query result Q4 of 15
Step-by-Step Solution
Solution:
Step 1: Understand GROUP BY with HAVING COUNT(*) > 1
This query groups rows by email and filters groups with more than one row, i.e., duplicates.Step 2: Determine the output
The query returns emails that appear multiple times in the employees table.Final Answer:
All emails that appear more than once in employees -> Option BQuick Check:
HAVING COUNT(*) > 1 filters duplicates [OK]
Quick Trick: HAVING filters groups after grouping, unlike WHERE [OK]
Common Mistakes:
- Thinking WHERE filters groups
- Assuming unique emails are included
- Expecting syntax error without WHERE
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