SELECT max(Market_Value_in_Billion) ,  min(Market_Value_in_Billion) FROM company
What is the maximum and minimum market value of companies?
[Schema (values) (types)]: | company_employee |  people : people_id (text) , age (number) , name (number) , nationality (text) , graduation_college (text) | company : company_id (text) , name (number) , headquarters (number) , industry (text) , sales_in_billion (text) , profits_in_billion (text) , assets_in_billion (number) , market_value_in_billion (text) | employment : company_id (text) , people_id (number) , year_working (number);