What should be taken into consideration when using group by in SQL?

When using GROUP BY, it is important to consider the following points:

1. The GROUP BY clause should be used after the SELECT clause but before the WHERE clause.
2. Every column in the SELECT clause must be either a column in the GROUP BY clause, a parameter in an aggregate function, or a constant.
3. The order of columns in the GROUP BY clause can impact the results of the grouping.
4. If aggregate functions, such as SUM, COUNT, AVG, are used in the SELECT clause, in addition to using the GROUP BY clause, the HAVING clause can also be used to filter the aggregated results.
5. The HAVING clause is used after the WHERE clause to filter the aggregated results.
6. If multiple columns are used in the GROUP BY clause, the results will be grouped in the order of those columns.