当我使用ActiveRecord::Base.connection.execute运行直接原始sql时，dev和prod服务器正在生成不同类型的结果，尽管两者都是正确的。
QUERY（在rails控制台中）：
query = ActiveRecord::Base.connection.execute("SELECT courses.name as course, round(count(placements.id)*100/count(students.id),2) as placed, count(placements.id) as total FROM courses LEFT JOIN students ON courses.id = students.course_id LEFT JOIN placements ON placements.student_id = students.id where students.course_id<>1 group by course")
DEV SERVER ：
#<Mysql2::Result:0xab44ca4 @query_options={:as=>:array, :async=>false, :cast_booleans=>false, :symbolize_keys=>false, :database_timezone=>:utc, :application_timezone=>nil, :cache_rows=>true, :connect_flags=>-2147442171, :cast=>true, :default_file=>nil, :default_group=>nil, :adapter=>"mysql2", :pool=>5, :timeout=>5000, :encoding=>"utf8", :database=>"ietplacementdb_dev", :username=>"ietplacementuser", :password=>"placement@pass15", :socket=>"/var/run/mysqld/mysqld.sock", :flags=>2}>
query.as_json
[["M.C.A.", "2.0", 1], ["M.Tech.", "20.0", 2]]
PROD SERVER：
[{"course"=>"M.C.A.", "placed"=>0.0, "total"=>0, 0=>"M.C.A.", 1=>0.0, 2=>0}, {"course"=>"M.Tech.", "placed"=>0.0, "total"=>0, 0=>"M.Tech.", 1=>0.0, 2=>0}]
query.as_json
[{"course"=>"M.C.A.", "placed"=>0.0, "total"=>0, "0"=>"M.C.A.", "1"=>0.0, "2"=>0}, {"course"=>"M.Tech.", "placed"=>0.0, "total"=>0, "0"=>"M.Tech.", "1"=>0.0, "2"=>0}]