如果你正在使用oracle…STRING将被创建为VARCHAR(255)列，TEXT将被创建为CLOB。

NATIVE_DATABASE_TYPES = {
    primary_key: "NUMBER(38) NOT NULL PRIMARY KEY",
    string: { name: "VARCHAR2", limit: 255 },
    text: { name: "CLOB" },
    ntext: { name: "NCLOB" },
    integer: { name: "NUMBER", limit: 38 },
    float: { name: "BINARY_FLOAT" },
    decimal: { name: "DECIMAL" },
    datetime: { name: "TIMESTAMP" },
    timestamp: { name: "TIMESTAMP" },
    timestamptz: { name: "TIMESTAMP WITH TIME ZONE" },
    timestampltz: { name: "TIMESTAMP WITH LOCAL TIME ZONE" },
    time: { name: "TIMESTAMP" },
    date: { name: "DATE" },
    binary: { name: "BLOB" },
    boolean: { name: "NUMBER", limit: 1 },
    raw: { name: "RAW", limit: 2000 },
    bigint: { name: "NUMBER", limit: 19 }
}

https://github.com/rsim/oracle-enhanced/blob/master/lib/active_record/connection_adapters/oracle_enhanced_adapter.rb

如果大小固定且较小，则为字符串;如果大小可变且较大，则为文本。 这很重要，因为文本比字符串大得多。它包含更多的千字节。

所以对于小字段总是使用string(varchar)。字段。First_name，登录名，电子邮件，(文章或帖子的)主题 文本的例子:一篇文章或文章的内容或主体。段落等字段

字符串大小从1到255(默认值为255)

文本大小1到4294967296(默认值为65536

如果你正在使用oracle…STRING将被创建为VARCHAR(255)列，TEXT将被创建为CLOB。

NATIVE_DATABASE_TYPES = {
    primary_key: "NUMBER(38) NOT NULL PRIMARY KEY",
    string: { name: "VARCHAR2", limit: 255 },
    text: { name: "CLOB" },
    ntext: { name: "NCLOB" },
    integer: { name: "NUMBER", limit: 38 },
    float: { name: "BINARY_FLOAT" },
    decimal: { name: "DECIMAL" },
    datetime: { name: "TIMESTAMP" },
    timestamp: { name: "TIMESTAMP" },
    timestamptz: { name: "TIMESTAMP WITH TIME ZONE" },
    timestampltz: { name: "TIMESTAMP WITH LOCAL TIME ZONE" },
    time: { name: "TIMESTAMP" },
    date: { name: "DATE" },
    binary: { name: "BLOB" },
    boolean: { name: "NUMBER", limit: 1 },
    raw: { name: "RAW", limit: 2000 },
    bigint: { name: "NUMBER", limit: 19 }
}

https://github.com/rsim/oracle-enhanced/blob/master/lib/active_record/connection_adapters/oracle_enhanced_adapter.rb

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》

公认的答案是棒极了，它正确地解释了字符串和文本之间的区别(主要是数据库中的限制大小，但还有一些其他的陷阱)，但我想指出一个小问题，让我通过它，因为这个答案并没有完全为我做。

最大大小:limit => 1到4294967296不能完全按照放置的方式工作，我需要从最大大小到-1。我正在存储大型JSON blobs，有时它们可能非常大。

下面是我的迁移，使用了更大的值，MySQL不会抱怨这个值。

注意极限的末尾是5，而不是6

class ChangeUserSyncRecordDetailsToText < ActiveRecord::Migration[5.1]
  def up
    change_column :user_sync_records, :details, :text, :limit => 4294967295
  end

  def down
    change_column :user_sync_records, :details, :string, :limit => 1000
  end
end

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。