case when is null

CASE WHEN is null的作用是在查询结果中对字段进行条件判断，判断字段是否为null，并根据判断结果进行赋值。如果字段的值为null，则可以使用CASE WHEN is null来判断并进行相应的赋值操作。例如，可以使用以下方式来实现从数据表中选择一个字段"field"，如果"field"值是1或null，则赋值为1，其它情况为0：

CASE WHEN field = 1 OR field IS NULL THEN 1 ELSE 0 END

这样写可以实现对字段进行条件判断，并根据判断结果进行赋值操作。如果字段的值为1或null，则赋值为1，否则赋值为0。<span class="em">1</span><span class="em">2</span><span class="em">3</span>
#### 引用[.reference_title]
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