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 the 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 some of the various records set using the GROUP BY clause. The following example will sum up all the records related to a single person and you will have a total of 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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