n.无意义暗码;[电子] 零位(null的复数);
v.使无效;取消(null的单三形式);
例句:
The physical data type'% s'does not allow nulls.
物理数据类型'' %1!''不允许为空.
Nulls are not matched to any value, including other instances of null.
空值不与任何值匹配, 包括其他实例的空值.
An identity column or a column used in a primary key , cannot allow nulls.
标识列或主关键字中的列的值不能为空.