如果你使用postgres，尽可能使用文本，除非你有大小限制，因为文本vs varchar没有性能损失

There is no performance difference among these three types, apart from increased storage space when using the blank-padded type, and a few extra CPU cycles to check the length when storing into a length-constrained column. While character(n) has performance advantages in some other database systems, there is no such advantage in PostgreSQL; in fact character(n) is usually the slowest of the three because of its additional storage costs. In most situations text or character varying should be used instead

PostsgreSQL手册》

如上所述，不只是db数据类型，它也会影响将生成的视图，如果你是脚手架。 String将生成一个text_field text将生成一个text_area

如果属性在form中匹配f.text_field，则使用string，如果匹配f.text_area，则使用text。

如果你使用postgres，尽可能使用文本，除非你有大小限制，因为文本vs varchar没有性能损失

There is no performance difference among these three types, apart from increased storage space when using the blank-padded type, and a few extra CPU cycles to check the length when storing into a length-constrained column. While character(n) has performance advantages in some other database systems, there is no such advantage in PostgreSQL; in fact character(n) is usually the slowest of the three because of its additional storage costs. In most situations text or character varying should be used instead

PostsgreSQL手册》

区别在于如何将符号转换为查询语言中相应的列类型。

用MySQL:字符串映射到VARCHAR https://edgeguides.rubyonrails.org/active_record_migrations.html

:string |                   VARCHAR                | :limit => 1 to 255 (default = 255)  
:text   | TINYTEXT, TEXT, MEDIUMTEXT, or LONGTEXT2 | :limit => 1 to 4294967296 (default = 65536)

参考:

https://hub.packtpub.com/working-rails-activerecord-migrations-models-scaffolding-and-database-completion/

什么时候分别使用?

一般的经验法则是，使用:string作为短文本输入(用户名、电子邮件、密码、标题等)，使用:text作为较长的预期输入，如描述、评论内容等。

较短的字段使用字符串，如姓名，地址，电话，公司

对于较大的内容、评论、内容、段落使用Text。

我的一般规则是，如果是超过一行的内容，我通常会选择文本，如果是2-6个简短的单词，我就会选择字符串。

对于字符串，官方规则是255。因此，如果字符串超过255个字符，请使用text。