question: What is the earliest Year commissioned wiht an Average annual output greater than 58 and Installed capacity of 20?
answer: SELECT MIN(year_commissioned) FROM table_name_64 WHERE average_annual_output__million_kwh_ > 58 AND installed_capacity__megawatts_ = 20
context: CREATE TABLE table_name_64 (year_commissioned INTEGER, average_annual_output__million_kwh_ VARCHAR, installed_capacity__megawatts_ VARCHAR)