Sum() function is not working in MySql

MySQL SUM function is used to find out the sum of a field in various records.

To understand SUM function, consider an employee_tbl table, which is having the following records:

mysql> SELECT * FROM employee_tbl;
+------+------+------------+--------------------+
| id | name | work_date | daily_typing_pages |
+------+------+------------+--------------------+
| 1 | John | 2007-01-24 | 250 |
| 2 | Ram | 2007-05-27 | 220 |
| 3 | Jack | 2007-05-06 | 170 |
| 3 | Jack | 2007-04-06 | 100 |
| 4 | Jill | 2007-04-06 | 220 |
| 5 | Zara | 2007-06-06 | 300 |
| 5 | Zara | 2007-02-06 | 350 |
+------+------+------------+--------------------+
7 rows in set (0.00 sec)
Now, suppose based on the above table you want to calculate total of all the dialy_typing_pages, then you can do so by using the following command:

mysql> SELECT SUM(daily_typing_pages)
-> FROM employee_tbl;
+-------------------------+
| SUM(daily_typing_pages) |
+-------------------------+
| 1610 |
+-------------------------+
1 row in set (0.00 sec)
You can take sum of various records set using GROUP BY clause. Following example will sum up all the records related to a single person and you will have total typed pages by every person.

mysql> SELECT name, SUM(daily_typing_pages)
-> FROM employee_tbl GROUP BY name;
+------+-------------------------+
| name | SUM(daily_typing_pages) |
+------+-------------------------+
| Jack | 270 |
| Jill | 220 |
| John | 250 |
| Ram | 220 |
| Zara | 650 |
+------+-------------------------+
5 rows in set (0.17 sec)

:: Basic Mathod for Sum function is :: SELECT SUM(column_name) FROM table_name;

Now, I think you might get idea, but still if anything is missing then you can This[^], This[^] and This[^] Links.
I think it might be helpful to you.