How to remove columns in Rails 5

To remove a column from a table in Rails 5, run the following migration:

rails g migration RemoveFieldNameFromTableName field_name:datatype

Make sure to change the migration to use your column and table name. For instance,

rails g migration RemoveTitleFromPosts title:string

This will generate the following migration:

class RemoveTitleFromPosts < ActiveRecord::Migration[5.2]
def change
remove_column :posts, :title, :string

Then run rails db:migrate.