SQL for MSACCESS how to implement character delimited data hierarchy? - sql

Question

Say, there's a flattened sequential hierarchy table with a special character "+" denoting hierarchy level
hr_table
ID FIELD1 My irrelevant comments
----------------
1 ASSETS No pluses - it means level0 hierarchy
2 +ASSETS_01 Level1 hierarchy
3 ++345667654 Level2 hierarchy
4 ++563255512 Level2 hierarchy
5 ...
Is there a way to create field structure in MSACCESS using SQL? I am trying to structure final data as follows:
final_data_table
ID LEVEL0 LEVEL1 LEVEL2 ...
-------------------------------------------
1 ASSETS ASSETS_01 345667654
2 ASSETS ASSETS_01 563255512
Any/all help greatly appreciated!

Answer 1

Curiosity got the better of me so I explored query approach. I resorted to using domain aggregate functions. Be aware domain aggregate functions can perform slowly with large datasets. However, consider:
Query1:
SELECT hr_table.ID, IIf([Field1] Like "+*",Left([Field1],InStrRev([Field1],"+")),0) AS Prefix, IIf([Field1] Like "+*",Null,[Field1]) AS Asset1, IIf(InStrRev([Field1],"+")=1,Mid([Field1],2),Null) AS Asset2, IIf([Field1] Like "++*",Mid([Field1],InStrRev([Field1],"+")+1),Null) AS Data
FROM hr_table;
Query2:
SELECT Query1.ID, Query1.Prefix, DMax("Asset1","Query1","ID<=" & [ID]) AS A1, DMax("Asset2","Query1","ID<=" & [ID]) AS A2, Query1.Data
FROM Query1
WHERE ((Not (Query1.Data) Is Null));
Query3:
SELECT Query2.Prefix, Query2.A1, Query2.A2, Query2.Data, DCount("*","Query2","A1='" & [A1] & "' AND A2='" & [A2] & "' AND Prefix = '" & [Prefix] & "' AND ID<=" & [ID]) AS GrpSeq
FROM Query2;
Query4:
TRANSFORM Max(Query3.Data) AS MaxOfData
SELECT Query3.A1, Query3.A2, Query3.GrpSeq
FROM Query3
GROUP BY Query3.A1, Query3.A2, Query3.GrpSeq
PIVOT Query3.Prefix;
I am definitely not sure about treatment of Level3 and beyond. Could be VBA will be only way to resolve.

Answer 2

The following code has been tested and works with the data structure you have mentioned. It is currently set to handle up to 10 levels, but that can be easily changed. The tricky part was to NOT write out the record until you have all levels for that ONE row (New row starts with different level1 value, or when more than one level-n value provided). The final row is written after eof of input.
Option Compare Database
Option Explicit
Function Parse_Fields()
Dim dbs As DAO.Database
Dim rsIN As DAO.recordSet
Dim rsOUT As DAO.recordSet
Dim i As Integer
Dim iPlus As Integer
Dim aLevels(10)
Dim bAdding As Boolean
Set dbs = CurrentDb
Set rsIN = dbs.OpenRecordset("hr_table")
Set rsOUT = dbs.OpenRecordset("final_data_table")
bAdding = False
Do While Not rsIN.EOF
'Debug.Print "Input: " & rsIN!field1
If left(rsIN!field1, 1) <> "+" Then
' Check if not first time thru... if not, write prior levels..
If bAdding = True Then
rsOUT.Update
End If
iPlus = 0
rsOUT.AddNew
rsOUT!Level0 = rsIN!field1
bAdding = True
' Don't issue the .Update yet! Wait until another Level0 or EOF.
Else
For iPlus = 1 To 10 ' Change code if more than ten levels
If Mid(rsIN!field1, iPlus, 1) <> "+" Then Exit For
Next iPlus
' Check if same level as previous! If so, do NOT overlay!
If Not IsNull(rsOUT.Fields(iPlus)) Then
For i = 1 To iPlus - 1 ' Save the proper levels for the new record.
aLevels(i) = rsOUT.Fields(i)
Next i
rsOUT.Update ' Need to write out record.
rsOUT.AddNew
For i = 1 To iPlus ' Populate the new record with prior levels
rsOUT.Fields(i) = aLevels(i)
Next i
rsOUT.Fields(iPlus) = Mid(rsIN!field1, iPlus) ' Add the new level
Else
rsOUT.Fields(iPlus) = Mid(rsIN!field1, iPlus)
End If
End If
rsIN.MoveNext ' Get next input
Loop
' Need to write out the final record we have beenbuilding!
rsOUT.Update
rsIN.Close
rsOUT.Close
Set rsIN = Nothing
Set rsOUT = Nothing
Set dbs = Nothing
Debug.Print "FINISHED!!"
End Function