varchar 字段 - 两个的幂是否更有效? [英] varchar Fields - Is a Power of Two More Efficient?

问题描述

使用大小为 2 的幂的 varchar 字段比另一个数字更有效吗?我想不是，因为对于 SQL Server，默认值为 50.

Is it more efficient to use a varchar field sized as a power of two vs. another number? I'm thinking no, because for SQL Server the default is 50.

但是，我听说(但从未证实)将字段大小设置为 2 的幂更有效，因为它们等同于偶数字节，并且计算机以位为单位进行处理字节.

However, I've heard (but never confirmed) that sizing fields as a power of 2 is more efficient because they equate to even bytes, and computers process in bits & bytes.

那么，声明为 varchar(32) 或 varchar(64) 的字段是否比 varchar(50) 有任何真正的好处?

So, does a field declared as varchar(32) or varchar(64) have any real benefit over varchar(50)?

推荐答案

没有

在其他一些用途中，使用具有 2 次幂大小的结构有一些优势，主要是因为您可以将这些(2 的幂)的数量放入另一个大小为 2 的幂的结构中.但这不适用于 DB 字段大小.

In some other uses, there are some advantages to use structures with a power of two size, mostly because you can fit a nice (power of two) number of these inside another power-of-two-sized structure. But this doesn't apply to a DB fieldsize.

与 VARCHAR 相关的唯一二次幂大小是关于 varchar 的确切类型(或某些 SQL 方言中的 TEXT/BLOB):如果它小于 256，它可以使用单个字节来表示长度.如果小于65536(64KB)，两个字节就够了，三个字节到16777216(16MB)，四个字节到4294967296(4GB).

The only power-of-two-sizing related to VARCHARs is about the exact type of varchar (or TEXT/BLOB in some SQL dialects): if it's less than 256, it can use a single byte to indicate length. if it's less than 65536 (64KB), two bytes are enough, three bytes work up to 16777216 (16MB), four bytes go to 4294967296 (4GB).

此外，可以说 VARCHAR(50) 与 VARCHAR(255) 一样昂贵，因为两者都需要 n+1 字节的存储空间.

Also, it can be argued that VARCHAR(50) is just as expensive as VARCHAR(255), since both will need n+1 bytes of storage.

当然那是在考虑 Unicode 之前...

Of course that's before thinking of Unicode...

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