我们如何在 MySQL SELECT 查询中将组函数与非组字段一起使用？

如果我们想在 SELECT 查询中对非分组字段使用分组函数，则必须使用 GROUP BY 子句。一般语法可以如下

语法

SELECT group_function1,…, non-group-column1,… from table_name GROUP BY column_name;

示例

mysql> Select COUNT(*), id from Student GROUP BY id;
+----------+------+
| COUNT(*) | id   |
+----------+------+
| 1        | 1    |
| 1        | 2    |
| 1        | 15   |
| 1        | 17   |
| 1        | 20   |
+----------+------+
5 rows in set (0.00 sec)
mysql> Select COUNT(*), address from Student GROUP BY id;
+----------+---------+
| COUNT(*) | address |
+----------+---------+
| 1        | Delhi   |
| 1        | Mumbai  |
| 1        | Delhi   |
| 1        | Shimla  |
| 1        | Jaipur  |
+----------+---------+
5 rows in set (0.00 sec)

GROUP BY 子句后的字段可以与 SELECT 查询中给出的非组字段不同。