user: Question: What is the lowest 2006 metropolitan population for a mexico city, mexico with a GDP per capita of less than 20300?
Columns: ['Rank', 'Metropolitan area', 'Country', 'GDP (PPP) (2008) Billions of US$', 'Metropolitan population (2006) Millions', 'GDP (PPP) US$ per capita']
Types: ['real', 'text', 'text', 'real', 'real', 'real']
Sample row: [1.0, 'Mexico City', 'Mexico', 390.0, 21.2, 20300.0]
SQL:

assistant: SELECT MIN("Metropolitan population (2006) Millions") FROM "Table" WHERE "Country" = 'mexico' AND "Metropolitan area" = 'mexico city' AND "GDP (PPP) US$ per capita" < 20300.0;