mysql数据库 text类型的长度限制,使用change_column来进行长度的修改并不影响原有数据

在我的概念中，mysql中的text字段应该是没有长度限制的，但是今天事实告诉我，text类型的长度是有限制的。其中mysql的text类型有64K长度限制的，MEDIUMTEXT中型是2G，LONGTEXT大型是4G .

Creating MEDIUMTEXT columns in MySQL using Rails

BY AMY ON 2010.01.23 AT 15:11 ·FILED UNDER COMPUTERS, PROGRAMMING

Adapted from http://www.depixelate.com/2008/5/24/rails-migrations-for-large-text-columns:

  create_table :foo do |t|
    ...
    t.text     :new_col, :limit => 64.kilobytes + 1
    ...
  end

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Leave a CommentCreating MEDIUMTEXT columns in MySQL using Rails

BY AMY ON 2010.01.23 AT 15:11 ·FILED UNDER COMPUTERS, PROGRAMMING

Adapted from http://www.depixelate.com/2008/5/24/rails-migrations-for-large-text-columns:

  create_table :foo do |t|
    ...
    t.text     :new_col, :limit => 64.kilobytes + 1
    ...
  end

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mysql text类型 长度不够的问题

2006-05-27  作者:amao  同分类文章 

description:

转一篇文章存入数据库只能显示全面一部分，

ALTER TABLE fib_blog CHANGE content content LONGTEXT NOT NULL

修改数据库，然后看看  .htaccess使用指南    利用这个来让blog静态化。就像bbs.chinahtml.com一样

1.1 Migrations are Classes

A migration is a subclass of ActiveRecord::Migration that implements two class methods: up(perform the required transformations) and down (revert them).

Active Record provides methods that perform common data definition tasks in a database independent way (you’ll read about them in detail later):

• create_table
• change_table
• drop_table
• add_column
• change_column
• rename_column
• remove_column
• add_index
• remove_index

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i found mysql text type has 64k limit,and for my application,it's not enough,so how to migrate from text to mediumtext,also i want keep my original data well

mysql text types schema alert

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asked 1 hour ago mlzboy 54518 81% accept rate

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1 Answer

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alter table foo modify column bar mediumtext; link|edit|flag

     change_column :urls,:content,:text,:limit=>128.kilobytes

• change_column(table_name, column_name, type, options): Changes the column to a different type using the same parameters as add_column.

http://api.rubyonrails.org/classes/ActiveRecord/Migration.html

http://guides.rubyonrails.org/migrations.html

ActiveRecord::Migration.upgrade_table :subtitles do |t|
t.integer :video_id, :null => false
end

这个方法写在rake里，以后就不用migration了，要不然文件太多了，是朋友教我的，呵呵