SQL GROUP BY 子句与 SELECT 语句结合在一起使用，可以将相同数据分成一组。
在 SELECT 语句中，GROUP BY 子句紧随 WHERE 子句，在 ORDER BY 子句之前。
语法：
GROUP BY 子句的基本语法如下所示。GROUP BY 子句必须在 WHERE 子句的条件之后，ORDER BY 子句（如果有的话）之前。
SELECT column1, column2
FROM table_name
WHERE [ conditions ]
GROUP BY column1, column2
ORDER BY column1, column2示例：
考虑含有如下所示记录的 CUSTOMERS 表：
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Khilan | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | Chaitali | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+如果你想要知道每个客户的薪水如何，可以写一个带有 GROUP BY 子句的查询：
SQL> SELECT NAME, SUM(SALARY) FROM CUSTOMERS
GROUP BY NAME;结果如下所示：
+----------+-------------+
| NAME | SUM(SALARY) |
+----------+-------------+
| Chaitali | 6500.00 |
| Hardik | 8500.00 |
| kaushik | 2000.00 |
| Khilan | 1500.00 |
| Komal | 4500.00 |
| Muffy | 10000.00 |
| Ramesh | 2000.00 |
+----------+-------------+现在，让我们换一张 CUSTOMERS 表，表中记录的 NAME 字段有重复值：
+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2000.00 |
| 2 | Ramesh | 25 | Delhi | 1500.00 |
| 3 | kaushik | 23 | Kota | 2000.00 |
| 4 | kaushik | 25 | Mumbai | 6500.00 |
| 5 | Hardik | 27 | Bhopal | 8500.00 |
| 6 | Komal | 22 | MP | 4500.00 |
| 7 | Muffy | 24 | Indore | 10000.00 |
+----+----------+-----+-----------+----------+同样，如果你想要知道每个客户的薪水如何的话，可以写一个带有 GROUP BY 子句的查询：