我正在构建一个mongo数据库，用于存储带有时间戳的数据。我数据库中的每个文档都有一个时间字段：
{"time":<datetime-object>}
我已经为time字段创建了索引：
self.db.test.create_index([("time", pymongo.ASCENDING)])
并执行一个查询，该查询仅从数据库请求时间戳信息：
self.db.test.find({'time':{'$gte':start, '$lte':end}}, {"time":1, "_id":0}).sort([("time", 1)])
我还阅读了其他问题/文档，说使用索引来获取文档应按排序顺序返回文档，因为索引本身已被排序，但是我看到的所有示例仍然直接调用{{1} }作为查询的一部分。我的问题是，如果我仅从数据库中仅请求一个我有索引的字段，我是否需要在查询中包括sort()方法，还是将文件按排序顺序返回？
答案 0 :(得分：1)
如果我仅从数据库中仅请求一个具有索引的字段，我是否需要在我的查询中包括sort（）方法，还是将文档按排序顺序返回？
在示例single field中，其中索引为covered query的情况下，返回的顺序就是索引本身的顺序。
但是，对于带有multikey index的多键字段，情况并非如此。这是因为多键索引无法覆盖对数组字段的查询。
由于以下原因，建议指定sort()
query planner如果能够使用索引，则会自动放弃排序阶段。有关更多信息，另请参见Query Optimisation和Explain Results。
明确指定Sub FindFormatting()
Dim Found As Range
Application.FindFormat.Clear
Application.FindFormat.Interior.Color = RGB(0, 106, 130)
Set Found = FindAll(What:="", SearchWhat:=ActiveSheet, LookIn:=xlFormulas, LookAt:=xlPart, SearchFormat:=True)
If Not Found Is Nothing Then Found.Font.Color = RGB(255, 255, 255)
Application.FindFormat.Interior.Color = RGB(0, 138, 170)
Set Found = FindAll(What:="", SearchWhat:=ActiveSheet, LookIn:=xlFormulas, LookAt:=xlPart, SearchFormat:=True)
If Not Found Is Nothing Then Found.Font.Color = RGB(255, 255, 255)
Application.FindFormat.Interior.Color = RGB(177, 209, 217)
Set Found = FindAll(What:="", SearchWhat:=ActiveSheet, LookIn:=xlFormulas, LookAt:=xlPart, SearchFormat:=True)
If Not Found Is Nothing Then Found.Font.Color = RGB(0, 0, 0)
Application.FindFormat.Interior.Color = RGB(204, 225, 230)
Set Found = FindAll(What:="", SearchWhat:=ActiveSheet, LookIn:=xlFormulas, LookAt:=xlPart, SearchFormat:=True)
If Not Found Is Nothing Then Found.Font.Color = RGB(0, 0, 0)
End Sub
Function FindAll(What, _
Optional SearchWhat As Variant, _
Optional LookIn, _
Optional LookAt, _
Optional SearchOrder, _
Optional SearchDirection As XlSearchDirection = xlNext, _
Optional MatchCase As Boolean = False, _
Optional MatchByte, _
Optional SearchFormat) As Range
'LookIn can be xlValues or xlFormulas, _
LookAt can be xlWhole or xlPart, _
SearchOrder can be xlByRows or xlByColumns, _
SearchDirection can be xlNext, xlPrevious, _
MatchCase, MatchByte, and SearchFormat can be True or False. _
Before using SearchFormat = True, specify the appropriate settings for the Application.FindFormat _
object; e.g. Application.FindFormat.NumberFormat = "General;-General;""-"""
Dim SrcRange As Range
If IsMissing(SearchWhat) Then
Set SrcRange = ActiveSheet.UsedRange
ElseIf TypeOf SearchWhat Is Range Then
Set SrcRange = IIf(SearchWhat.Cells.Count = 1, SearchWhat.Parent.UsedRange, SearchWhat)
ElseIf TypeOf SearchWhat Is Worksheet Then
Set SrcRange = SearchWhat.UsedRange
Else: SrcRange = ActiveSheet.UsedRange
End If
If SrcRange Is Nothing Then Exit Function
'get the first matching cell in the range first
With SrcRange.Areas(SrcRange.Areas.Count)
Dim FirstCell As Range: Set FirstCell = .Cells(.Cells.Count)
End With
Dim CurrRange As Range: Set CurrRange = SrcRange.Find(What:=What, After:=FirstCell, LookIn:=LookIn, LookAt:=LookAt, _
SearchDirection:=SearchDirection, MatchCase:=MatchCase, MatchByte:=MatchByte, SearchFormat:=SearchFormat)
If Not CurrRange Is Nothing Then
Set FindAll = CurrRange
Do
Set CurrRange = SrcRange.Find(What:=What, After:=CurrRange, LookIn:=LookIn, LookAt:=LookAt, _
SearchDirection:=SearchDirection, MatchCase:=MatchCase, MatchByte:=MatchByte, SearchFormat:=SearchFormat)
If CurrRange Is Nothing Then Exit Do
If Application.Intersect(FindAll, CurrRange) Is Nothing Then
Set FindAll = Application.Union(FindAll, CurrRange)
Else: Exit Do
End If
Loop
End If
End Function
不仅可以保护您的代码以防意外（例如，不一致的值等），还可以使代码可读。