请再帮助分析?下列两组代码
Dim g As New GroupTableBuilder("统计表1", DataTables("订单"))
g.Groups.AddDef("日期", DateGroupEnum.Year, "年")
g.Groups.AddDef("日期", "月")
g.Totals.AddDef("数量")
g.SamePeriodGrowth = True
g.Build()
MainTable = Tables("统计表1")
Dim g As New GroupTableBuilder("统计表1", DataTables("订单"))
g.Groups.AddDef("年")
g.Groups.AddDef("月")
g.Totals.AddDef("数量")
g.SamePeriodGrowth = True
g.Build()
MainTable = Tables("统计表1")
为什么第一组出现“同比增长“,而第二组不出现”同比增长“