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PostgreSQL HAVING

The HAVING clause is similar to WHERE but applies to aggregated data grouped by GROUP BY. It filters groups based on aggregate function results.

Key Topics

1. Basic Syntax

Use HAVING after GROUP BY:

SELECT department, COUNT(*) AS dept_count
FROM employees
GROUP BY department
HAVING COUNT(*) > 10;

This returns only departments with more than 10 employees.

2. Example Usage

SELECT department, AVG(salary) as avg_salary
FROM employees
GROUP BY department
HAVING AVG(salary) > 50000;

This filters out departments whose average salary is 50,000 or less.

Best Practices

  • Use HAVING to filter groups after GROUP BY is applied.
  • Only reference aggregate functions or grouped columns in HAVING.

Key Takeaways

  • HAVING is used in conjunction with GROUP BY to filter aggregated data.
  • It functions similarly to WHERE but for grouped results.
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