Table: bulgarian_badminton_champs_2
Columns: year
men_s_singles
women_s_singles
men_s_doubles
women_s_doubles
mixed_doubles

Question: Who won Women's doubles when Raina Tzvetkova won women's singles before 2000?
SQL: SELECT "women_s_doubles" FROM bulgarian_badminton_champs_2 WHERE "year" < 2000 AND "women_s_singles" = 'raina tzvetkova'

Question: Who won men's singles when petya nedelcheva diana dimova won women's doubles and vladimir metodiev krasimir yankov won men's doubles?
SQL: SELECT "men_s_singles" FROM bulgarian_badminton_champs_2 WHERE "women_s_doubles" = 'petya nedelcheva diana dimova' AND "men_s_doubles" = 'vladimir metodiev krasimir yankov'

Question: Who won men's singles when petya nedelcheva won women's singles, petya nedelcheva diana dimova won women's doubles, stilian makarski diana dimova won mixed doubles, and stilian makarski peyo boichinov won men's doubles?
SQL: SELECT "men_s_singles" FROM bulgarian_badminton_champs_2 WHERE "women_s_singles" = 'petya nedelcheva' AND "women_s_doubles" = 'petya nedelcheva diana dimova' AND "mixed_doubles" = 'stilian makarski diana dimova' AND "men_s_doubles" = 'stilian makarski peyo boichinov'

Question: Who won women's singles in 1986?
SQL: SELECT "women_s_singles" FROM bulgarian_badminton_champs_2 WHERE "year" = 1986