null adj. 1.無效力的,無束縛力的。 2.無效的,無用的,無益的;無價值的。 3.沒特征[個性]的,沒表情的。 4.〔罕用語〕不存在的,沒有的;零(位)的;空的。 n. 【數(shù)學】零,零位;空;【無線電】零訊號,微弱訊號。 a null indicator 零示器;零位指示器。 the null method 衡消法。 null and void 【律】無效;失效(This check is null and void. 本支票無效)。 vt. 使無效。
If a set contains no elements we shall designate it by Ф and define it as the empty or null set . 如果一個集合不包含元素,我們就把它記為,且定義它為空集或零集。
Set null sets the value to null if all foreign key columns for the table can accept null values 設置空如果表的所有外鍵列都可接受空值,則將該值設置為空。
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 如果對行的更新違反了某個約束或規(guī)則,或違反了對列的null設置,或者新值是不兼容的數(shù)據(jù)類型,則取消該語句、返回錯誤并且不更新任何記錄。
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 實踐證明采用熱管式真空集熱器與吸收式制冷機相結合的太陽能空調(diào)技術方案是成功的,它為太陽能光熱利用技術開辟了一個新的應用領域。
英文解釋
a set that is empty; a set with no members
百科解釋
In mathematics, a null set is a set that is negligible in some sense. For different applications, the meaning of "negligible" varies.