在创建 MySQL 视图时如何使用逻辑运算符？

使用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真。在下面的示例中，我们创建了一个基于'AND'运算符的视图。

示例

基本表是Student_info，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)

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)

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使用 OR 运算符的视图

我们知道，逻辑 OR 运算符会比较两个表达式，如果至少其中一个表达式为 true，则返回 true。在以下示例中，我们将创建一个具有基于“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)

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带有 NOT 运算符的视图

NOT 是唯一只接受一个操作数的运算符。如果操作数为 TRUE，则返回 0；如果操作数为 FALSE，则返回 1。在以下示例中，我们将创建一个具有基于“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)

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