SUM函數(shù)用于找出表中記錄在某字段處的總和。
要理解 SUM 函數(shù),請(qǐng)考慮 employee_tbl 表,表中記錄如下所示:
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)
現(xiàn)在,假設(shè)你想要獲取 daily_typing_pages 的總和,那么你可以用如下命令來(lái)達(dá)到目的:
SQL> SELECT SUM(daily_typing_pages)
-> FROM employee_tbl;
+-------------------------+
| SUM(daily_typing_pages) |
+-------------------------+
| 1610 |
+-------------------------+
1 row in set (0.00 sec)
你還可以使用 GROUP BY 子句來(lái)得出不同記錄分組的總和。下面的例子將會(huì)計(jì)算得出每個(gè)人的總和,,你將能夠得到每個(gè)人每天打的總頁(yè)數(shù)。
SQL> SELECT name, SUM(daily_typing_pages)
-> FROM employee_tbl GROUP BY name;