nullable

A database is one of the most important places to use nullable types .

数据库是使用可空类型的最重要的地方之一。

Library Support for nullable types , including conversion operators and arithmetic operators

为可空类型提供类库支持，包括转换运算符和算术运算符

Previously , the code would allow default behavior to occur when handling nullable fields .

以前，代码允许在处理可为空的域时采用缺省的行为。

Only the role field the one that had a default value of user passed the implicit nullable constraint .

只有role字段其默认值为user通过隐含的nullable约束。

Use nullable types to represent things that exist or do not exist depending on the circumstance .

根据具体环境，使用可空类型来表示存在或不存在的事物。

If nullable , it will contain the NULL value .

如果可为空，它将包含NULL值。

Type the specified nullable type .

指定的可空类型。

The DB2Types classes also provide a means to represent DB2 database column values as individual nullable objects .

DB2Types类型还提供了将DB2数据库列值表示为一个个可以为空的对象的方法。

A table should avoid nullable columns .

表应避免可为空的列。

Newly added not nullable column ( s ) are involved in the primary key or unique index ( constraint ) .

新添加的不可空列包含在主键或唯一索引（约束）中。

That represents the nullable type .

表示可空类型的。

Though most Rails developers do not like to keep constraints in the database , you should consider things like nullable columns .

虽然大多数Rails开发人员都不喜欢在数据库中保留限制，但您应该考虑像空列这样的事情。

Specifically , any type defined as Nullable ( Of T ) wasn 't allowed to be optional .

特别地，定义为Nullable（OfT）的任何类型都不允许是可选的。

If you use a nullable VARGRAPHIC column instead , the1021-byte index limitation is still true .

如果使用可空的VARGRAPHIC列，那么1021字节的索引限制仍然是对的。

Unfortunately the strongly-typed DataRow classes generated by Visual Studio do not use nullable types .

不幸的是，VisualStudio生成的强类型数据集（strongly-typedDataRow）并没有使用nullablevalues。

The metadata API also provides the ability to define nullable columns , establish primary keys , and set-up relationships between tables .

该元数据API还提供了定义可以为空的列的能力，并设置了表之间的关系。

I recently ran MoMA on SubSonic and found only one issue-a weird use of Nullable types .

最近我在SubSonic上运行了MoMA，只发现了一个问题&Nullable类型的一个奇怪应用。

Invalid length specified for this nullable datatype .

为该可为空的数据类型指定的长度无效。

If the column is NULLABLE , any number of NULLs can be inserted in that column .

如果此列可以包含NULL值，就可以在此列中插入任意数量的NULL值。

There is one major concern regarding this second strategy : in order for it to work , you must set all non-shared columns to NULLABLE .

关于第二个策略，有一个需要重点考虑的地方：为了让它工作，必须把所有非共享列设置为NULLABLE。

In C # you can flag a value type as a nullable type by adding ? after the type ( like int ? x ;) .

在C中，你可以在一个允许为空的值类型后面加上一个问号（比如，int？x；）。

In this example , no one is allowed to update or insert into that column , which is also marked as unique and not nullable .

在本例中，不允许任何人更新或插入同样标记为唯一和不得为空的列。

Column ' % s ' cannot be excluded from a vertical partition because it is neither nullable nor defined with a default value .

列''%1！''不能从垂直分区内排除，因为该列既不可为空，也没有定义默认值。

Nullable types and null coalescing operator

可置空类型和空合并运算符

It 's the list of field names , types , and optional additional information ( like the size , nullable , etc. ) that adds some complexity .

它是字段名称、类型和可选附加信息（如大小、nullable）的列表，这些可选附加信息会使名称变得比较复杂。

In the lower right part of the section , set all key columns of the output link to non-nullable by selecting No in the nullable column .

在本部分的右下侧，通过选择空列上的No可将所有输出链接的关键列都设置为非空。

Be sure to add a constraint that allows the new field to be both blank ( in the HTML form ) and nullable ( in the database ) .

注意要添加一个约束，使这个新字段同时为blank（在HTML表单中）和nullable（在数据库中）。

Incidentally you might wonder what nullable is all about ; that will become clearer when I discuss processing relative XPaths in a later column .

顺便说一句，您可能想知道nullable究竟是什么；在我于以后的专栏文章中讨论相对XPath的处理之后，您就会逐渐明白了。

Not only does it have the same " null reference exception " that Java had , with generics we also were given the problems with Nullable value types .

它不仅提供了Java所拥有的“空引用异常”，而且还提供了Nullable值类型以解决通用的问题。

The pros include compact tables ( no unnecessary nullable columns ), data partitions across three subclass tables and easy association with other tables using the top super class table .

优点包括数据表比较紧凑（没有不需要的可空字段），数据跨三个子类的表进行分区，容易使用超类的表与其他表进行关联。