How many cities have a stadium that was opened before the year of 2006?
CREATE TABLE stadium (city VARCHAR, opening_year INTEGER)
SELECT COUNT(DISTINCT city) FROM stadium WHERE opening_year < 2006
### Context: CREATE TABLE stadium (city VARCHAR, opening_year INTEGER) ### Question: How many cities have a stadium that was opened before the year of 2006? ### Answer: SELECT COUNT(DISTINCT city) FROM stadium WHERE opening_year < 2006