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_name_68 (year INTEGER, position VARCHAR, competition VARCHAR)

### Question ###
What is the sum of Year(s), when Postion is 6th, and when Competition is Commonwealth Games?

### Accurate SQL ###

SELECT SUM(year) FROM table_name_68 WHERE position = "6th" AND competition = "commonwealth games"