MySQL 如何使用GROUP BY子句创建MySQL视图？

我们可以使用 GROUP BY 从一列中分组值，并且如果需要，我们可以对该列执行计算。您可以在分组的列上使用COUNT、SUM、AVG等函数。为了理解带有视图的GROUP BY子句，我们使用基表’Student_info’创建一个名为’Info’的视图，其具有以下数据-

mysql> Select * from Student_info;
+------+---------+------------+------------+
| id   | Name    | Address    | Subject    |
+------+---------+------------+------------+
| 101  | YashPal | Amritsar   | History    |
| 105  | Gaurav  | Chandigarh | Literature |
| 125  | Raman   | Shimla     | Computers  |
| 130  | Ram     | Jhansi     | Computers  |
| 132  | Shyam   | Chandigarh | Economics  |
| 133  | Mohan   | Delhi      | Computers  |
+------+---------+------------+------------+
6 rows in set (0.00 sec)

阅读更多：MySQL 教程

Syntax

Create or Replace View view_name AS Select_statements FROM table GROUP BY expression1, expression2, ... expression_n;

示例

mysql> Create or Replace View Info AS select Subject, COUNT(*) FROM Student_info GROUP BY Subject;
Query OK, 0 rows affected (0.10 sec)

mysql> Select * from info;
+------------+----------+
| Subject    | COUNT(*) |
+------------+----------+
| Computers  |    3     |
| Economics  |    1     |
| History    |    1     |
| Literature |    1     |
+------------+----------+
4 rows in set (0.00 sec)

mysql> Create or Replace View Info AS select Subject,Name, COUNT(Subject) FROM Student_info GROUP BY Subject, Name;
Query OK, 0 rows affected (0.05 sec)

上面的查询将在GROUP BY子句中有两列。

mysql> Select * from info;
+------------+---------+----------------+
| Subject    | Name    | COUNT(Subject) |
+------------+---------+----------------+
| Computers  | Mohan   |       1        |
| Computers  | Ram     |       1        |
| Computers  | Raman   |       1        |
| Economics  | Shyam   |       1        |
| History    | YashPal |       1        |
| Literature | Gaurav  |       1        |
+------------+---------+----------------+
6 rows in set (0.00 sec)

上面的结果集表明，GROUP BY子句通过列的值将一组行分组成一组摘要行。