MySQL 如何在MySQL SELECT查询中使用非组字段的聚合函数？

如果我们想要在SELECT查询中使用非组字段的聚合函数，我们必须使用GROUP BY子句。通用语法如下所示

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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。