В чем разница между оператором WHERE и оператором HAVING в SQL?

The WHERE operator is used for filtering rows before they are grouped. The HAVING operator is used for filtering groups after they have been created by the GROUP BY operator.

Main differences:

Attribute	WHERE	HAVING
Purpose	Filters rows before grouping	Filters groups after grouping
Application	Applied to individual rows	Applied to aggregated group data
Execution	Executed before GROUP BY	Executed after GROUP BY
Columns	Uses table columns	Uses table columns and aggregate functions

Example with WHERE:

-- Select user names where age is greater than 18
SELECT name
FROM users
WHERE age > 18;

Example with HAVING:

-- Select departments where the average salary exceeds 50,000
SELECT department, AVG(salary)
FROM employees
GROUP BY department
HAVING AVG(salary) > 50000;

Example with both operators:

-- Select departments where the average salary of employees over 30 exceeds 60,000
SELECT department, AVG(salary)
FROM employees
WHERE age > 30
GROUP BY department
HAVING AVG(salary) > 60000;