是varchar，对吧?所以不管你用50个还是25个，为了安全起见，最好用50个，我认为我见过的最长的是19个左右。姓更长

我通常会选择:

名字:30个字符 姓氏:30个字符 电子邮件:50个字符 地址:200个字符

如果我担心名称字段太长，我有时也会将名称字段设置为50，因为现在存储空间很少成为问题。

W3C推荐:

If designing a form or database that will accept names from people with a variety of backgrounds, you should ask yourself whether you really need to have separate fields for given name and family name. … Bear in mind that names in some cultures can be quite a lot longer than your own. … Avoid limiting the field size for names in your database. In particular, do not assume that a four-character Japanese name in UTF-8 will fit in four bytes – you are likely to actually need 12. https://www.w3.org/International/questions/qa-personal-names

对于数据库字段，VARCHAR(255)是一个安全的默认选择，除非您确实有充分的理由使用其他选项。对于典型的web应用程序，性能不是问题。不要过早地优化。

是varchar，对吧?所以不管你用50个还是25个，为了安全起见，最好用50个，我认为我见过的最长的是19个左右。姓更长

这些可能对某人有用;

youtube max channel length = 20
facebook max name length   = 50
twitter max handle length  = 15
email max length           = 255 

http://www.interoadvisory.com/2015/08/6-areas-inside-of-linkedin-with-character-limits/

+------------+---------------+---------------------------------+
|   Field    | Length (Char) |           Description           |
+------------+---------------+---------------------------------+
|firstname   | 35            |                                 |
|lastname    | 35            |                                 |
|email       | 255           |                                 |
|url         | 60+           | According to server and browser |
|city        | 45            |                                 |
|address     | 90            |                                 |
+------------+---------------+---------------------------------+

编辑:增加了一些间距