我有一张看起来有点像这样的表：
date | timestamp | predicted_value
2017-10-25| 21758494903 | 0.1
2017-10-26| 21758494903 | 7.7
....
我希望能够使用单个查询按时间戳获取给定日期的最新predict_value。 I.E在我的输出中我想要：
Predictions.objects.all().order_by(
'-timestamp'
).values(
'date'
).annotate(
prediction=F('predicted_value')
)
我认为它应该是这样的：
F这会起作用吗？ Public Function copydata(forma As Form, i As Integer)
Dim dtb As DAO.Database
Dim tabl As Recordset
Dim flag As Boolean
Set dtb = CurrentDb
Set tabl = dtb.OpenRecordset("SamplesProcessing")
forma.Refresh
With tabl
Do Until flag = True
.MoveFirst
Do Until .EOF
If !SampleN = i Then
flag = True
.Edit
Select Case forma!Procedure
Case 1 'Before treatment
![W of raw sample] = forma!SampleMass
![ChemTreat operator] = forma!UserName
Case 2 'Fraction
![W of fraction used] = forma!SampleMass
![ChemTreat operator] = forma!UserName
Case 3 'After first burnng
![W after opened carbonisation] = forma!SampleMass
![ChemTreat operator] = forma!UserName
Case 4 'After second burning
![W after closed carbonisation] = forma!SampleMass
![ChemTreat operator] = forma!UserName
Case 5 'After chem treatment
![W after chem treatment] = forma!SampleMass
![ChemTreat operator] = forma!UserName
![HCl treatment] = True
Case 6 'Combustion
![W of C for reaction] = forma!SampleMass
![W of Li for reaction] = forma!LiMass
![Synthesis operator] = forma!UserName
Case 7 'Distillating
![W of BenzeneAndScint] = forma!BenzeneMass
![PercentofBenzene] = forma!BenzenePercent
![Distilaltion operator] = forma!UserName
Case 8 'Synthesis
![Synthesis operator] = forma!UserName
Case 9 'H2SO4 treatment
![H2SO4 treatment] = True
Case 10 'HCl treatment
![HCl treatment] = True
Case 11 'KOH treatment
![KOH treatment] = True
End Select
If IsNull(forma![ProcDate]) = False Then
!LastOperDate = forma![ProcDate]
End If
If IsNull(forma!Comments) = False Then
If IsNull(!Comments) = True Then
!Comments = forma!Comments
Else
!Comments = !Comments + "; " + forma!Comments
End If
End If
.Update
If .EOF = True Then
flag = False
End If
End If
.MoveNext
Loop
If flag = False Then
.AddNew
!SampleN = i
.Update
End If
Loop
End With
Set tabl = Nothing
End Function
会选择聚合中找到的第一个值，还是不能以这种方式使用它？