MySQL 如何在创建MySQL视图时使用逻辑运算符？

使用逻辑运算符如AND、OR和NOT可以创建MySQL视图，下面是一些示例。

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带AND运算符的视图

我们知道逻辑AND运算符比较两个表达式，如果两个表达式都为真则返回true。在下面的示例中，我们创建了一个带有基于AND运算符的条件的视图。

示例

基本表为Student_info，包含以下数据 –

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)

mysql> Create or Replace View Info AS select ID, Name, Address , Subject FROM Student_info WHERE (Subject = 'Computers' AND ADDRESS = 'DELHI');
Query OK, 0 rows affected (0.13 sec)

mysql> Select * from Info;
+------+-------+---------+-----------+
| ID   | Name  | Address | Subject   |
+------+-------+---------+-----------+
| 133  | Mohan | Delhi   | Computers |
+------+-------+---------+-----------+
1 row in set (0.00 sec)

带OR运算符的视图

我们知道逻辑OR运算符比较两个表达式，如果至少有一个表达式为真，则返回true。在下面的示例中，我们创建了一个带有基于OR运算符的条件的视图。

示例

mysql> Create or Replace View Info AS select ID, Name, Address , Subject FROM Student_info WHERE (Subject = 'Computers' OR ADDRESS = 'Amritsar');
Query OK, 0 rows affected (0.06 sec)

mysql> Select * from Info;
+------+---------+----------+-----------+
| ID   | Name    | Address  | Subject   |
+------+---------+----------+-----------+
| 101  | YashPal | Amritsar | History   |
| 125  | Raman   | Shimla   | Computers |
| 130  | Ram     | Jhansi   | Computers |
| 133  | Mohan   | Delhi    | Computers |
+------+---------+----------+-----------+
4 rows in set (0.00 sec)

带NOT运算符的视图

NOT是唯一只有一个操作数的运算符。如果操作数为TRUE，它返回0；如果操作数为FALSE，它返回1。在下面的示例中，我们创建了一个带有基于NOT运算符的条件的视图。

示例

mysql> Create or Replace View Info AS select ID, Name, Address , Subject FROM Student_info WHERE Subject != 'Computers';
Query OK, 0 rows affected (0.06 sec)

mysql> Select * from info;
+------+---------+------------+------------+
| ID   | Name    | Address    | Subject    |
+------+---------+------------+------------+
| 101  | YashPal | Amritsar   | History    |
| 105  | Gaurav  | Chandigarh | Literature |
| 132  | Shyam   | Chandigarh | Economics  |
+------+---------+------------+------------+
3 rows in set (0.00 sec)