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 stadium ( capacity INTEGER, opening_year VARCHAR )

### Question ###
What is the average capacity of the stadiums that were opened in year 2005?

### Accurate SQL ###

SELECT AVG(capacity) FROM stadium WHERE opening_year = 2005