SQL group by usage and group by syntax

In the SQL SQL Aggregate functions that use the same number of statements together provide some database tutorial columns for grouping (the result dataset method ).

GROUP

 

 

The best way to use SQLGROUPStatement example.

The following database table is called EmployeeHours to store the daily time of each employee:

Employee	Date	Hours
John Smith	5/6/2004	8
Allan Babel	5/6/2004	8
Tina Crown	5/6/2004	8
John Smith	5/7/2004	9
Allan Babel	5/7/2004	8
Tina Crown	5/7/2004	10
John Smith	5/8/2004	8
Allan Babel	5/8/2004	8
Tina Crown	5/8/2004	9

If the company manager wants to overlay all the work hours of all employees, he needs to execute the following SQL statement:

Select sum (Hours)
FROM EmployeeHours

But what if the manager wants to get the sum of his employees for every time?
Therefore, he needs to modify his SQL query and useGROUPStatement:

SELECT Employee, SUM (Hours)
FROM EmployeeHours
Group by Employee

The result of the SQL expression will be the following:

Employee	Hours
John Smith	25
Allan Babel	24
Tina Crown	27

 

As you can see, we only work for each employee, because we are grouped by the employee column.

The SQLGroup by sub-Statement can be used for other SQL Aggregate functions, such as AVG of SQL:

SELECT Employee, AVG (Hours)
FROM EmployeeHours
Group by Employee

Employee	Hours
John Smith	8.33
Allan Babel	8
Tina Crown	9

In the date column of our employee table, we can also group to find out what is the total number of hours from the date of each job to the table:

SELECT Date, SUM (Hours)
FROM EmployeeHours
Group by Date

Here is the result of the above SQL expression:

Date	Hours
5/6/2004	24
5/7/2004	27
5/8/2004	25