Add Remove A Database Column From A Table as a Rails TIL

rails/remove-a-database-column-from-a-table.md

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+# Remove A Database Column From A Table
+
+The `ActiveRecord` migration DSL includes a method
+[`remove_column`](https://api.rubyonrails.org/v7.0.3.1/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-remove_column)
+that can be used to remove an existing column from a table.
+
+It can be used like so, to remove the `sign_in_count` column from the `users`
+table.
+
+```ruby
+def change
+  remove_column :users, :sign_in_count
+end
+```
+
+Though that will work fine, you'll run into an `IrreversibleMigration` error if
+you try to `rails db:rollback`. It usually a good bet to make migrations
+reversible when it is easy to do so.
+
+All we need in order to make this migration reversible is to add the column
+type.
+
+```ruby
+def change
+  remove_column :users, :sign_in_count, :integer
+end
+```
+
+Now you can rollback (or [migrate up-down-up](migrating-up-down-up.md)) no
+problem.
+
+Keep in mind that only the structural changes are reversible. When you remove
+the column, all of the data goes with it, and that cannot be undone with a
+simple rollback.