null adj. 1.無(wú)效力的,無(wú)束縛力的。 2.無(wú)效的,無(wú)用的,無(wú)益的;無(wú)價(jià)值的。 3.沒(méi)特征[個(gè)性]的,沒(méi)表情的。 4.〔罕用語(yǔ)〕不存在的,沒(méi)有的;零(位)的;空的。 n. 【數(shù)學(xué)】零,零位;空;【無(wú)線(xiàn)電】零訊號(hào),微弱訊號(hào)。 a null indicator 零示器;零位指示器。 the null method 衡消法。 null and void 【律】無(wú)效;失效(This check is null and void. 本支票無(wú)效)。 vt. 使無(wú)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(gè)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(shè)置空如果表的所有外鍵列都可接受空值,則將該值設(shè)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(duì)行的更新違反了某個(gè)約束或規(guī)則,或違反了對(duì)列的null設(shè)置,或者新值是不兼容的數(shù)據(jù)類(lèi)型,則取消該語(yǔ)句、返回錯(cuò)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(shí)踐證明采用熱管式真空集熱器與吸收式制冷機(jī)相結(jié)合的太陽(yáng)能空調(diào)技術(shù)方案是成功的,它為太陽(yáng)能光熱利用技術(shù)開(kāi)辟了一個(gè)新的應(yīng)用領(lǐng)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.