Table: tennis_aces_2
Columns: aces
player
opponent
year
event
sets
result

Question: what's the earliest year that serena williams had more than 2 sets?
SQL: SELECT MIN("year") FROM tennis_aces_2 WHERE "player" = 'serena williams' AND "sets" > 2

Question: what's the earliest year that the wimbledon opponent was zheng jie?
SQL: SELECT MIN("year") FROM tennis_aces_2 WHERE "event" = 'wimbledon' AND "opponent" = 'zheng jie'

Question: what year was the opponent caroline garcia?
SQL: SELECT SUM("year") FROM tennis_aces_2 WHERE "opponent" = 'caroline garcia'

Question: what's the most recent year that samantha stosur was the opponent with 20 aces and having played more than 2 sets?
SQL: SELECT MAX("year") FROM tennis_aces_2 WHERE "aces" = 20 AND "opponent" = 'samantha stosur' AND "sets" > 2

Question: what year was the memphis event?
SQL: SELECT SUM("year") FROM tennis_aces_2 WHERE "event" = 'memphis'