Query group statistics (chapter summary)

1. Five grouping functions are provided in SQL: Count (), AVG (), sum (), min (), and Max.


2. The group by clause can be used to group data, while the having clause can be used to filter the grouped data again.


3. Multiple grouping fields can be created at the same time during grouping.


4. Grouping can be used not only for entity tables, but also for temporary tables to be queried.


5. The grouping function allows nesting, but no fields, including grouping fields, can appear in the nested grouping query.