PostgreSQL 范围类型中的无穷大"是什么意思?将 infinity 或 -infinity 指定为界限或 NULL 之间有什么区别吗?IE.infinity 是指定范围限制为无限的显式形式,而 NULL 会隐式指定无限限制范围吗?
What is the meaning of 'infinity' in PostgreSQL range types? Is there any difference between specifying infinity or -infinity as a bound, or NULL? I.e. is infinity an explicit form of specifying that the range bound is infinite, whereas NULL would implicit specify an infinite bound range?
请参阅以下示例:
SELECT tstzrange('-infinity','infinity') && tstzrange(NULL, NULL); ?column? ---------- t SELECT tstzrange('2013-01-01 00:00:00+01', '2013-02-01 00:00:00+01') && tstzrange(NULL, '2013-03-01 00:00:00+01'); ?column? ---------- t SELECT tstzrange('2013-01-01 00:00:00+01', '2013-02-01 00:00:00+01') && tstzrange('-infinity', '2013-03-01 00:00:00+01'); ?column? ---------- t 推荐答案更新:稍后再看,更好的解释:
Update: See this later, better explanation:
- 当范围类型中的 NULL 边界在功能上等效时,为什么 PostgreSQL 会认为它们与无限边界不同?
NULL 对 重叠做同样的事情运算符 && 分别为 -infinity 或 infinity.我在这里引用手册:
NULL does the same thing for the overlap operator && as -infinity or infinity, respectively. I quote the manual here:
对任一边界使用 NULL 会导致该边的范围无界.
Using NULL for either bound causes the range to be unbounded on that side.
但是作为value,NULL还是有别于'infinity'!
But as value, NULL is still distinct from 'infinity'!
SELECT tstzrange('-infinity','infinity') = tstzrange(NULL, NULL);返回 FALSE(不是 NULL,请注意!).
Returns FALSE (not NULL, mind you!).
更多内容请参见 SQLfiddle.
More in this SQLfiddle.
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PostgreSQL 范围类型中的 NULL 与 `infinity`
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