外键可以让您将一张表中的一行与另一张表中的一行相关起来。

Foreign keys allow you to relate a row in one table with a row in another.

在这一部分中，您将看到如何生成为每一个用户会话存储数据所用的键。

In this section, you see how to generate keys that let you store data for each user session.

它确实对于值和键长度有一些限制，但可以在代码中轻松地调整那些限制。

It does have some limitations on value and key lengths, but those are easily adjustable in the code.

So we can have four total hydrogens bonding here, - and we can think about how to describe these carbon- carbon bonds.

我们这里一共有四个氢原子成键，我们可以考虑怎么来-,描述碳碳键。

So in addition to having these two carbon bonds, we actually also have four carbon hydrogen bonds in addition to our carbon-carbon bonds.

在这碳碳之间的键以外，我们还有四个碳氢键,除了我们的碳碳键外。

Well, if this bond has completely identically equal sharing of electrons, then this bond will be nonpolar.

如果一根键连的两个原子,对键上的电子吸引程度是完全等价的，那么这根键是非极性的。