GZDBHelper中ExecuteScalar方法，执行SQL语句，返回第一行第一列

/// <summary>
/// 执行SQL语句，返回第一行第一列
/// </summary>
/// <typeparam name="T">返回类型</typeparam>
/// <param name="sql">SQL语句</param>
/// <param name="parameters">查询参数</param>
/// <returns></returns>
T ExecuteScalar<T>(string sql, IDbParms parameters);