inserting big decimals as strings works consistently among dbs, so use string form

activerecord/lib/active_record/connection_adapters/abstract/quoting.rb

@@ -66,7 +66,7 @@ module ActiveRecord
           end
           # BigDecimals need to be put in a non-normalized form and quoted.
         when nil        then nil
-        when BigDecimal then value.to_f
+        when BigDecimal then value.to_s('F')
         when Numeric    then value
         when Date, Time then quoted_date(value)
         when Symbol     then value.to_s

activerecord/test/cases/adapters/sqlite3/quoting_test.rb

@@ -67,7 +67,7 @@ module ActiveRecord
 
         def test_type_cast_bigdecimal
           bd = BigDecimal.new '10.0'
-          assert_equal bd.to_f, @conn.type_cast(bd, nil)
+          assert_equal bd.to_s('F'), @conn.type_cast(bd, nil)
         end
 
         def test_type_cast_unknown