Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_203_640 ( id number, "name" text, "college" text, "years" text, "reign" text )

### Question ###
how long was harald v of norway the king of norway at the university of oxford ?

### Accurate SQL ###

SELECT "years" - "years" FROM table_203_640 WHERE "name" = 'harald v of norway'