Migrations will raise an exception if there are multiple column definitions (same name).

1 files changed, 6 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index 5f090d16cd..582ac516c7 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -356,8 +356,12 @@ module ActiveRecord
         type = type.to_sym if type
         options = options.dup
 
-        if @columns_hash[name] && @columns_hash[name].primary_key?
-          raise ArgumentError, "you can't redefine the primary key column '#{name}'. To define a custom primary key, pass { id: false } to create_table."
+        if @columns_hash[name]
+          if @columns_hash[name].primary_key?
+            raise ArgumentError, "you can't redefine the primary key column '#{name}'. To define a custom primary key, pass { id: false } to create_table."
+          else
+            raise ArgumentError, "you can't define an already defined column '#{name}'."
+          end
         end
 
         index_options = options.delete(:index)