What is the method of using group by in a database?

The GROUP BY statement is used to group the result set by one or more columns. It is often used with aggregate functions such as SUM, COUNT, AVG, etc. Using GROUP BY allows the result set to be divided into multiple groups based on the specified columns, and apply aggregate functions to each group to get the statistical results for each group.

The syntax for GROUP BY is as follows:

Select column 1, column 2, …, column n from table name and group by column 1, column 2, …, column n.

The columns labeled as Column 1, Column 2, …, Column n are the specified columns to be grouped.

For example, the following example groups the employee table by department and calculates the number of employees in each department.

Show the department and the number of employees in each department from the employees table.

In the example above, group by department and use the COUNT(*) function to calculate the number of employees in each group. The result will return each department and its number of employees.