Add documentation

Author: aidanharan

README.md

@@ -186,6 +186,19 @@ The removal of duplicates happens during the SQL query.
 
 Because of this implementation, if you pass `on_duplicate` to `upsert_all`, make sure to assign your value to `target.[column_name]` (e.g. `target.status = GREATEST(target.status, 1)`). To access the values that you want to upsert, use `source.[column_name]`.
 
+#### Computed Columns
+
+The adapter supports computed columns. They can either be virtual `stored: false` (default) and persisted `stored: true`. You can create a computed column in a migration like so:
+
+```ruby
+create_table :users do |t|
+  t.string :name
+  t.virtual :lower_name, as: "LOWER(name)", stored: false
+  t.virtual :upper_name, as: "UPPER(name)", stored: true
+  t.virtual :name_length, as: "LEN(name)"
+end
+```
+
 ## New Rails Applications
 
 When creating a new Rails application you need to perform the following steps to connect a Rails application to a

lib/active_record/connection_adapters/sqlserver/schema_statements.rb

@@ -94,7 +94,7 @@ def columns(table_name)
           end
         end
 
-        def new_column_from_field(table_name, field, definitions)
+        def new_column_from_field(_table_name, field, _definitions)
           sqlserver_options = field.slice(:ordinal_position, :is_primary, :is_identity, :table_name)
           sql_type_metadata = fetch_type_metadata(field[:type], sqlserver_options)
           generated_type = extract_generated_type(field)