error in select Query

i have this table in Database

Student Table





and i want to do select query to select the studentID and summation of all students’ grade

i try to do this using this Query

   $selectedStudents = Yii::app()->db->createCommand()

                           ->select('studentID' ,

                           ('Mathgrade' + 'physicsgrade').' As TotalGrads')


                          ->queryAll() ;

but when thus Query was executed i get this error

CDbCommand failed to execute the SQL statement: SQLSTATE[42S22]: Column not found: 1054 Unknown column ‘0’ in ‘field list’. The SQL statement executed was: SELECT 0

FROM student

i dont know what is error please can any one help me thank in advanced

Check your syntax in the call to the select() function…

Spoiler: what is the result of: (‘Mathgrade’ + ‘physicsgrade’).’ As TotalGrads’