列表过滤条件

public override void PrepareFilterParameter(Kingdee.BOS.Core.List.PlugIn.Args.FilterArgs e)
{
long userId = this.Context.UserId;
string filter = @" exists(select * from z_ta frole
where frole.FUser=" + this.View.Context.UserId + @" and frole.fambdept=FSecondAMBUnit and frole.FCostitem=FCOSTITEM )";
e.FilterString = e.FilterString.IsNullOrEmpty() ? filter : e.FilterString + " and " + filter;
}
写了一个插件,处理列表过滤.有2个字段,当这2个字段同时在另外一个表中有记录时,改记录才显示在列表中.目前的问题是这2个字段的列名都一样.在EXISTS中如何分辨开来