ดัชนี Happy Planet คือปีใด?ไม่จำเป็นต้องใช้ตารางทั้งหมด
What year is the happy planet index?It is not neccessary to use all the tables.
 table_77747:  "Index" [ text]  "Organization" [ text]  "Year" [ real]  "Rank" [ text] 
SELECT SUM("Year") FROM table_77747 WHERE "Index" = 'happy planet index'