?? A Common SQL Learning Moment!
Today, I ran into an interesting SQL behavior while trying to fetch employees with the highest earnings. My original query looked something like this:
SELECT count(employee_id), salary * months AS earnings FROM employee GROUP BY earnings HAVING earnings = MAX(earnings);
Seems like it should work, right? ?? However, SQL doesn’t allow direct comparisons like MAX(earnings) in the HAVING clause because aggregate functions like MAX() must be processed separately.
After a bit of troubleshooting and learning, I realized that the solution involves a subquery to first calculate the maximum earnings, then use that result in the HAVING clause. Here's the corrected version:
SELECT COUNT(employee_id), salary * months AS earnings FROM employee GROUP BY earnings HAVING earnings = (SELECT MAX(salary * months) FROM employee);
?? Why does SQL behave this way?
SQL processes queries in specific steps: GROUP BY comes before HAVING, and aggregate functions like MAX() are calculated only after the grouping is done. That's why you need a subquery to pre-calculate the maximum value.
What started as a frustrating bug turned into a valuable learning experience! ??
?? Have you ever run into similar SQL challenges? Let’s discuss!
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