null set meaning in English

空集, 零集
零集

If a set contains no elements we shall designate it by Ф and define it as the empty or null set .
如果一个集合不包含元素，我们就把它记为，且定义它为空集或零集。
Set null sets the value to null if all foreign key columns for the table can accept null values
设置空如果表的所有外键列都可接受空值，则将该值设置为空。
If an update to a row violates a constraint or rule , violates the null setting for the column , or the new value is an incompatible data type , the statement is canceled , an error is returned , and no records are updated
如果对行的更新违反了某个约束或规则，或违反了对列的null设置，或者新值是不兼容的数据类型，则取消该语句、返回错误并且不更新任何记录。
The practice proved uses the hot tubular real null set to be hot the solar energy air conditioning technology plan which and the absorption type refrigerator unifies is successful , it opened a new application domain for the solar energy light heat utilization technology
实践证明采用热管式真空集热器与吸收式制冷机相结合的太阳能空调技术方案是成功的，它为太阳能光热利用技术开辟了一个新的应用领域。