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.
除非你有一個很特別的原因去使用 NULL 值，你應(yīng)該總是讓你的字段保持 NOT NULL。這看起來好像有點爭議，請往下看。
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.
這種校驗會通過拒絕空值，強迫加上非空[NOT NULL]字段的約束，但是也只有在這種情況下，你的數(shù)據(jù)庫會拒絕空值。
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，在通過非 NULL 值初始化陣列時或陣列增長超過它們當(dāng)前大小時，DB2 會隱式為陣列分配內(nèi)存。