同一表中兩條記錄之間的字段值差異

Question

我有table1，它有抄表字段。我想計算抄表RECORD1和抄表記錄2.

Answer 1

之間的差異假設你有table1連續ID場下面的查詢會給你想要的結果：

SELECT T1.ID, T1.MeterReading, T2.MeterReading, [T2].[MeterReading]-[T1].[MeterReading] AS Difference 
FROM tbl AS T1, tbl AS T2 
WHERE (((T1.ID)=[T2].[ID]-1)); 

但是，如果ID是autonumber類型，你可能會遺漏一些數字並失去連續性，所以我建議使用number類型的ID和使用一些代碼來確保連續性。

Answer 2

我假設了表和字段的名稱，所以顯然你應該改變這些以適應你的模式。

Dim rs AS new ADODB.Recordset 
Dim PrevReading AS Long 

rs.CursorLocation = adUseClient 
rs.Open "SELECT * FROM tblReadings ORDER BY ReadingDate",CurrentProject.Connection,adOpenKeyset, adLockOptimistic 
Do While Not rs.Eof 
    rs.Field("Difference")=rs.Field("MeterReading") - PrevReading 
    PrevReading = rs.Fields("MeterReading") 
    rs.MoveNext 
Loop 
rs.Close