Even though this question seems to be quite old, will post an answer for someone who reaches in here searching.
SET @count = 0;
UPDATE `users` SET `users`.`id` = @count:= @count + 1;
If the column is used as a foreign key in other tables, make sure you use ON UPDATE CASCADE
instead of the default ON UPDATE NO ACTION
for the foreign key relationship in those tables.
Further, in order to reset the AUTO_INCREMENT
count, you can immediately issue the following statement.
ALTER TABLE `users` AUTO_INCREMENT = 1;
For MySQLs it will reset the value to MAX(id) + 1
.
rename_column :table, :old_column, :new_column
You'll probably want to create a separate migration to do this. (Rename FixColumnName
as you will.):
script/generate migration FixColumnName
# creates db/migrate/xxxxxxxxxx_fix_column_name.rb
Then edit the migration to do your will:
# db/migrate/xxxxxxxxxx_fix_column_name.rb
class FixColumnName < ActiveRecord::Migration
def self.up
rename_column :table_name, :old_column, :new_column
end
def self.down
# rename back if you need or do something else or do nothing
end
end
For Rails 3.1 use:
While, the up
and down
methods still apply, Rails 3.1 receives a change
method that "knows how to migrate your database and reverse it when the migration is rolled back without the need to write a separate down method".
See "Active Record Migrations" for more information.
rails g migration FixColumnName
class FixColumnName < ActiveRecord::Migration
def change
rename_column :table_name, :old_column, :new_column
end
end
If you happen to have a whole bunch of columns to rename, or something that would have required repeating the table name over and over again:
rename_column :table_name, :old_column1, :new_column1
rename_column :table_name, :old_column2, :new_column2
...
You could use change_table
to keep things a little neater:
class FixColumnNames < ActiveRecord::Migration
def change
change_table :table_name do |t|
t.rename :old_column1, :new_column1
t.rename :old_column2, :new_column2
...
end
end
end
Then just db:migrate
as usual or however you go about your business.
For Rails 4:
While creating a Migration
for renaming a column, Rails 4 generates a change
method instead of up
and down
as mentioned in the above section. The generated change
method is:
$ > rails g migration ChangeColumnName
which will create a migration file similar to:
class ChangeColumnName < ActiveRecord::Migration
def change
rename_column :table_name, :old_column, :new_column
end
end
Best Answer
You need to execute an SQL statement.
you can entry manually in your migration
Note this is just an example. The final SQL statement syntax depends on the database.