Question: Give the percentage of Japanese suppliers whose account is in debt.
SQL: SELECT CAST(SUM(IIF(T2.n_name = 'JAPAN', 1, 0)) AS REAL) * 100 / COUNT(T1.s_name) FROM supplier AS T1 INNER JOIN nation AS T2 ON T1.s_nationkey = T2.n_nationkey WHERE T1.s_acctbal < 0