Table: ittf_pro_tour_winners_6
Columns: year_location
mens_singles
womens_singles
mens_doubles
womens_doubles

Question: Who won the mens doubles at the 2006 guangzhou event?
SQL: SELECT "mens_doubles" FROM ittf_pro_tour_winners_6 WHERE "year_location" = '2006 Guangzhou'

Question: How many times was the womens doubles in china?
SQL: SELECT COUNT("mens_singles") FROM ittf_pro_tour_winners_6 WHERE "womens_doubles" = 'China'

Question: How many times did  li ju win the womens singles and wang liqin win the mens singles?
SQL: SELECT COUNT("womens_doubles") FROM ittf_pro_tour_winners_6 WHERE "womens_singles" = 'Li Ju' AND "mens_singles" = 'Wang Liqin'