Объясните пожалуйста "на пальцах", как это работает:

SELECT T_INSTITUTION_1.name, Sum(T_DATA.GR1) AS [Sum-GR1], Sum(T_DATA.GR3) AS [Sum-GR3]
FROM (T_INSTITUTION INNER JOIN T_DATA ON T_INSTITUTION.ID = T_DATA.ID)
INNER JOIN T_INSTITUTION AS T_INSTITUTION_1
ON T_INSTITUTION.PARENT_ID = T_INSTITUTION_1.ID
WHERE (((T_DATA.ID_Row)=17) AND ((T_DATA.ID_Section)=1))
GROUP BY T_INSTITUTION_1.name;

http://www.sql.ru/forum/1078646/pomogite-novichku-razobratsya