当一个变化是一个关系，相关的外键的属性设置为空值。

When a change is made to a relationship, the related foreign-key property is set to a null value.

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注意：在清单6中，我们还将两个显示参数(title和border)设置为空值。

NOTE: in listing 6, notice that we also set two display parameters (title and border) to empty values.

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在DB 2 for i 6.1发布之前，SQL Update和insert语句能够使用一个值为- 1的指示符变量，将支持空值的列设置为空值。

Prior to the DB2 for I 6.1 release, SQL Update and Insert statements could use an indicator variable with a value of -1 to set a null capable column to the null value.

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