/// <summary>
 /// MySql group_concat(distinct .. order by .. separator ..)
 /// </summary>
 /// <param name="column"></param>
 /// <returns></returns>
 public static IGroupConcat GroupConcat(object column) => SqlExtExtensions.GroupConcat(column);
 /// <summary>
 /// case when .. then .. end
 /// </summary>
 /// <returns></returns>
 public static ICaseWhenEnd Case() => SqlExtExtensions.Case();