为什么varchar(254)而不是varchar(255)?

Why do so many developers set varchar to 254 and not 255 when creating MySQL tables?

为什么许多开发人员在创建MySQL表时将varchar设置为254而不是255 ?

Proof that this happens: mysql varchar 254

这一点的证明:mysql varchar 254

2 个解决方案

#1

varchar fields require n+1 bytes for fields less than or equal to 255 and required n+2 bytes for fields > 255

varchar字段对于小于或等于255的字段需要n+1字节，对于字段> 255需要n+2字节

http://dev.mysql.com/doc/refman/5.0/en/storage-requirements.html

It should be set to 255, I'm assuming developers think they will save an extra byte from 254, but 255 is the standard

它应该设置为255，我假设开发人员认为他们会从254节省一个字节，但是255是标准

#2

Your Google query gave you the hints already. One of the first hits is this:

您的谷歌查询已经给出了提示。第一个热门话题是:

https://www.vbulletin.com/forum/project.php?issueid=32655

It basically says, that FULLTEXT indexes on VARCHAR(255) require twice the space of a VARCHAR(254) FULLTEXT index. And some more other bloat on top of that.

它基本上说，VARCHAR(255)上的全文索引需要VARCHAR(254)的两倍空间。除此之外，还有一些其他的膨胀。

I think this is far more important than saving one byte in the data table.

我认为这比在数据表中保存一个字节要重要得多。

#1