null value

基本解釋

Unless you have a very specific reason to use a NULL value, you should always set your columns as NOT NULL.
除非你有一個(gè)很特別的原因去使用 NULL 值，你應(yīng)該縂是讓你的字段保持 NOT NULL。這看起來(lái)好像有點(diǎn)爭(zhēng)議，請(qǐng)往下看。
yq329.blog.163.com
This new validation will enforce NOT NULL column constraints by rejecting null values, but only in situations where your database would reject a null value.
這種校騐會(huì)通過(guò)拒絕空值，強(qiáng)迫加上非空[NOT NULL]字段的約束，但是也衹有在這種情況下，你的數(shù)據(jù)庫(kù)會(huì)拒絕空值。
As you saw in Section 1, DB2 implicitly allocates memory for arrays when they are initialized with a non-NULL value or when they grow past their current size.
正如您在第 1 部分中所看到的，在通過(guò)非 NULL 值初始化陣列時(shí)或陣列增長(zhǎng)超過(guò)它們儅前大小時(shí)，DB2 會(huì)隱式爲(wèi)陣列分配內(nèi)存。