Table: tennis_match_stats_2
Columns: edition
round
date
against
surface
opponent
win_lose
result

Question: In what edition is Ungur's opponent David Nalbandian?
SQL: SELECT "edition" FROM tennis_match_stats_2 WHERE "opponent" = 'David Nalbandian'

Question: When was the win/lose lose and the round a play-off?
SQL: SELECT "date" FROM tennis_match_stats_2 WHERE "win_lose" = 'Lose' AND "round" = 'Play-off'

Question: In what round did he play against Sergiy Stakhovsky?
SQL: SELECT "round" FROM tennis_match_stats_2 WHERE "opponent" = 'Sergiy Stakhovsky'