SQL多表多条件查询

string sql="select * from StudentResult as A join Department as B on A.BMID=B.BMID join ExamInfor as C on A.BMID=C.BMID";
            ArrayList str = new ArrayList();  //用来判断是否为空，切记顺序与下面的StrSql列表相对应。
            str.Add(KSBM); str.Add(KSKM); str.Add(Point); str.Add(SJBH);

            ArrayList StrSql = new ArrayList();//用于添加上去了语句。
            StrSql.Add("A.BMID=" + KSBM);
            StrSql.Add("A.SJKM='" + KSKM + "'");
            StrSql.Add(Point);
            StrSql.Add("A.SJBH='" + SJBH + "'");

            int i = 0, flag = 0;  //引索。
            foreach (string s in str)
            {
                if (s != "" && flag == 0)
                { sql += " where " + StrSql[i].ToString(); flag = 1; }
                else
                {
                    if (s != "")
                    { sql += " and " + StrSql[i].ToString(); }
                }
                i++;
            }

            SqlDBHelper sqlhelp = new SqlDBHelper();
            return sqlhelp.RunSqlCommand(sql, "StudentResult");