Table: srebotnik_championships
Columns: outcome
year
championship
surface
partner
opponents_in_the_final
score_in_the_final

Question: What surface was played on when Piet Norval was a partner?
SQL: SELECT "surface" FROM srebotnik_championships WHERE "partner" = 'piet norval'

Question: What was the surface played on when they were a runner-up in 2007?
SQL: SELECT "surface" FROM srebotnik_championships WHERE "outcome" = 'runner-up' AND "year" = 2007