How does Oracle calculate multiple grouping conditions?

Oracle can use the GROUP BY clause to group data, and the HAVING clause to filter the grouped data. The general steps for using multiple grouping conditions for statistics are as follows:

1. Choose the columns to be calculated using the SELECT statement, and perform statistical operations on the data using functions such as COUNT, SUM, and AVG.
2. Specify the table you want to query in the FROM clause.
3. Specify the columns to group by in the GROUP BY clause. Multiple columns can be specified, separated by commas.
4. Specify filtering conditions in the HAVING clause. Aggregate functions can be used to filter data after grouping.

Here is an example query that calculates the number of employees and average salary for different departments in a table.

SELECT department, COUNT(*) AS employee_count, AVG(salary) AS avg_salary
FROM employees
GROUP BY department
HAVING COUNT(*) > 5 AND AVG(salary) > 5000;

This query will group employees by department, calculate the number of employees and average salary for each department. Then, it will use a HAVING clause to filter out departments with more than 5 employees and an average salary greater than 5000.