```ruby
require 'active_record/scoping/default'
require 'active_record/scoping/named'
require 'active_record/base'

module ActiveRecord
  class SchemaMigration < ActiveRecord::Base
    attr_accessible :version

    def self.table_name
      Base.table_name_prefix + 'schema_migrations' + Base.table_name_suffix
    end

    def self.create_table
      unless connection.table_exists?(table_name)
        connection.create_table(table_name, :id => false) do |t|
          t.column :version, :string, :null => false
        end
        connection.add_index table_name, :version, :unique => true,
          :name => "#{Base.table_name_prefix}unique_schema_migrations#{Base.table_name_suffix}"
      end
    end

    def self.drop_table
      if connection.table_exists?(table_name)
        connection.remove_index table_name, :name => "#{Base.table_name_prefix}unique_schema_migrations#{Base.table_name_suffix}"
        connection.drop_table(table_name)
      end
    end

    def version
      super.to_i
    end
  end
end
```

Remove duplicated unique index name.
user
```ruby
require 'active_record/scoping/default'
require 'active_record/scoping/named'
require 'active_record/base'

module ActiveRecord
  class SchemaMigration < ActiveRecord::Base
    attr_accessible :version

    def self.table_name
      "#{Base.table_name_prefix}schema_migrations#{Base.table_name_suffix}"
    end

    def self.index_name
      "#{Base.table_name_prefix}unique_schema_migrations#{Base.table_name_suffix}"
    end

    def self.create_table
      unless connection.table_exists?(table_name)
        connection.create_table(table_name, :id => false) do |t|
          t.column :version, :string, :null => false
        end
        connection.add_index table_name, :version, :unique => true, :name => index_name
      end
    end

    def self.drop_table
      if connection.table_exists?(table_name)
        connection.remove_index table_name, :name => index_name
        connection.drop_table(table_name)
      end
    end

    def version
      super.to_i
    end
  end
end
```
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