一、拼接字符串类型的字段
string sql = @"select distinct ziduan from tablename where ziduan in ('{0}')";
sql=string.Format(sql, string.Join("','", list.ToArray()));
二、拼接数字类型的字段
string sql = @"select distinct ziduan from tablename where ziduan in ({0})";
sql=string.Format(sql, string.Join(",", list.ToArray()));