SQL - SUM Function

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SQL 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:

SQL> 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:

SQL> 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.

SQL> 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)


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