By default, a column can contain a NULL value, but if you don't want that, you can append the "NOT NULL" postfix to the field definition.
默认情况下，列可以包含null值，但是，如果不想这样，可以在字段定义中附加“NOT NULL”后缀。
This new validation will enforce NOT null column constraints by rejecting null values, but only in situations where your database would reject a null value.
这种校验会通过拒绝空值，强迫加上非空[not NULL]字段的约束，但是也只有在这种情况下，你的数据库会拒绝空值。
If defined as NOT NULL, the value corresponds to the start time associated with the most recent transaction (the value of the as ROW BEGIN column).
如果定义为NOT NULL，该值会对应于与最近的事务相关联的开始时间(ASROW begin列的值)。
For example, if a before trigger supplies value to a NOT NULL column, then the before trigger is executed first and a value is supplied to the column so that the NOT NULL constraint isn't violated.
例如，如果一个BEFORE触发器给一个NOT null列提供值，那么先执行BEFORE触发器，给列提供值，所以不会违反NOT NULL约束。
The above error can occur if the Sybase existing table definition declares one of the columns to be NOT NULL but there is no value for that column in one of the records of the result set.
如果sybase现有表定义声明某一列为NOT NULL，但是在结果集中的某一行记录在那一列没有值，就可能发生上述错误。
The itemNumber column provides a unique identity for each item (or row) and has an attached column-level constraint that enforces a valid value to always be supplied (NOT NULL).
itemNumber列提供了每个商品（或列）的惟一标识，它上面还有列级约束，强制要求提供正确的值（NOT NULL）。
But in DB2, you must provide a value for NOT NULL columns in an INSERT statement when a default hasn't been defined.
但在DB 2中，如果未定义该值，则必须在insert语句中为NOT null列提供值。
But as we hope we've shown in the table, that really represents an array with a single element whose value is null, not a null array.
但是，正如我们希望的，在表中已经显示，它真正表示的是含有单一元素的数组，元素的值为“零”(null)，而不是一个“零”(null)数组。
We may not know what type t represents, but we know that the null literal is a valid value for any reference type.
我们可能不知道t类型代表什么，但我们知道null字母对任何引用类型而言是一个空值。
These are generally implicit design decisions in the APIs such as where a value can be null, or where a numeric value is not expected to be negative.
在API的设计中，有一些决策是不言而喻的，比如何时值可以为null，或者何时数字值不能为负。
This may be in the form of specific set values (for example, all 9's or 'Do Not Use') or blank values (where a blank represents a keystroke distinct from a null value).
这可能以特定的设置值(例如所有的9或‘DoNotUse’)或空白值(一个空白表示一个按键，这不同于一个null值)的形式出现。
For simplicity, we chose not to validate entries into the list by returning a value of null each time the validator is run.
为简单起见，我们选择不验证列表中的条目，每次运行检验器时返回空值。
If a default value is not specified, the variable is initialized to NULL.
如果没有指定默认值，则初始变量为NULL。
If the form input field is not null, set the payload you receive as the widget value, as shown in Listing 14.
如果表单输入字段不为空，将小部件的值设为接收到的负载，如清单14所示。
A general, good practice is not to allow null (that is, no value) columns in a relational database, because when you attempt to read such a column, you get a null value exception.
通常，一种优秀的实践就是不要在关系数据库中使用null(即没有值)列，因为当您试图读取这类列时，您将得到一个null值异常。
The default model binder also cannot assign a null value to a property that does not accept nulls. In particular, the model binder cannot assign a null value to the UnitsInStock property.
默认的模型绑定器同样不能指定一个null值到一个不允许为null的属性中，这里的情况是模型绑定其不能指定一个null值到UnitsInStock属性中。
Here the null or blank value does not represent incomplete data, but reflects that the business condition requiring the data has not yet occurred.
在这里，null或空白值并不表示不完整的数据，而是反映需要尚未出现的数据的业务情况。
Because null is not a valid default value for an annotation, I provide some basic defaults that can be easily tested for, so I can identify the value that was specified.
由于null不是标注的有效默认值，因此这里提供了一些便于测试的基本默认值，以便识别被指定的值。
IllegalArgumentError is thrown every time an argument is not considered valid, for example, when a null value is passed to a method as a parameter.
IllegalArgumentError在每次认为参数无效时抛出，例如，将null值作为参数传递给方法。
If the value of the transportTModelKey parameter is not null, then a transport categorization keyedReference is added; its value is the value of the transportTModelKey parameter.
如果transportTModelKey参数的值不为空，就添加一个传输类别 keyedReference ；它的值即是 transportTModelKey 参数的值。
It's the situation where, for instance, someone passes a null value to a method not coded to handle nulls.
比方说，把null值传入一个并未编写如何处理null值的方法中，这就是一种边界情况。
A workaround to this is to supply a default value to the not NULL column whose value comes from a BEFORE INSERT TRIGGER, so that the constraint is not violated.
一种解决方法是给从BEFORE INSERT触发器取得值的NOT null列提供默认值，这样就不会违反约束。
Note that when using OLAP data sources, you will not be able to use null in the else statement, and will need to use a static value.
注意，在使用olap数据源时，不能在else语句中使用null，需要使用一个静态值。
If the corresponding class, field, or method is not generic, a null value is passed when calling the method.
若相应的类、字段或方法非泛型，则在调用方法时将返回null值。
If this value is set to null or empty string, CLP throws a JCC exception: Column not updatable.
如果将这个值设置为null或空字符串，clp会抛出JCC异常：Column not updatable。
Notice in Listing 9 that the instance does have a valid (meaning it is not null) toAddress value.
注意在清单9 中，该实例确实有一个有效（意为非 nul ）的toAddress值。
When you specify the element directive to retrieve element-centric XML, if the column has a NULL value, the corresponding element is not generated by the EXPLICIT mode.
当指定ELEMENT指令检索以元素为中心的XML时，如果列具有NULL值，则EXPLICIT模式将不生成相应的元素。
If a NOT NULL constraint is specified, then the column must have a default value other than NULL.
如果规定一个不允许有空值是一个约束，那么字段必须有一个不同于空值的默认值。
NULL return value means the current thread has not captured the mouse. However, it is possible that another thread or process has captured the mouse.
尤其要注意，如果返回值为NULL并不一定就是说当前线程没有捕捉到鼠标，完全有可能是另一个线程或进程捕捉到了鼠标。
NULL return value means the current thread has not captured the mouse. However, it is possible that another thread or process has captured the mouse.
尤其要注意，如果返回值为NULL并不一定就是说当前线程没有捕捉到鼠标，完全有可能是另一个线程或进程捕捉到了鼠标。
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