检查表的字段是否在SQL中设置了NOT NULL属性？
要检查表的字段是否具有NOT NULL属性，可以使用两种语法中的任何一种。第一种语法如下-
desc yourTableName;
以下是第二种语法-
select column_name,is_nullable
from information_schema.columns
where table_schema = ‘yourDatabaseName’
and table_name = 'yourTableName’;
我们首先来看一个示例并创建一个表-
mysql> create table DemoTable(
StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY,
StudentName varchar(40),
StudentAge int NOT NULL,
IsActiveStudent ENUM('ACTIVE",INACTIVE') NOT NULL,
StudentCountryName varchar(40)
);
第一种语法如下，检查表的字段是否设置了NOT NULL属性-
mysql> desc DemoTable;
这将产生以下输出-
+--------------------+--------------------------+------+-----+---------+----------------+| Field | Type | Null | Key | Default | Extra |
+--------------------+--------------------------+------+-----+---------+----------------+
| StudentId | int(11) | NO | PRI | NULL | auto_increment |
| StudentName | varchar(40) | YES | | NULL | |
| StudentAge | int(11) | NO | | NULL | |
| IsActiveStudent | enum('ACTIVE",INACTIVE') | NO | | NULL | |
| StudentCountryName | varchar(40) | YES | | NULL | |
+--------------------+--------------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
第二种语法如下检查表的字段是否设置了NOT NULL属性-
mysql> select column_name,is_nullable
from information_schema.columns
where table_schema = 'web'
and table_name = 'DemoTable';
这将产生以下输出-
+--------------------+-------------+| COLUMN_NAME | IS_NULLABLE |
+--------------------+-------------+
| StudentId | NO |
| StudentName | YES |
| StudentAge | NO |
| IsActiveStudent | NO |
| StudentCountryName | YES |
+--------------------+-------------+
5 rows in set (0.00 sec)
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