Table: boston_badminton_1997
Columns: year
mens_singles
womens_singles
mens_doubles
womens_doubles
a_mixed_doubles
b_mixed_doubles

Question: What is the least year when men's singles is Raju Rai?
SQL: SELECT MIN("year") FROM boston_badminton_1997 WHERE "mens_singles" = 'Raju Rai'