Show the color of Barbera Grape?
select color from grapes where grape = "Barbera"
Show the grape which scores higher than 90?
select distinct grape from wine where score > 90
Show the grape whose white color grapes are used to produce wines?
select distinct t1.grape from grapes as t1 join wine as t2 on t1.grape = t2.grape where t1.color = "White"